Fingerprint sensor with bioimpedance indicator

ABSTRACT

An apparatus may include an ultrasonic sensor system, a platen, a set of bioimpedance electrodes proximate the platen and a control system configured for communication with the ultrasonic sensor system and the set of bioimpedance electrodes. The control system may be further configured for controlling the ultrasonic sensor system to transmit ultrasonic waves, receiving ultrasonic sensor signals from the ultrasonic sensor system corresponding to ultrasonic waves reflected from a portion of a body in contact with the platen, receiving bioimpedance measurements from the set of bioimpedance electrodes and estimating a status of one or more biometric indicators of the portion of the body based on the ultrasonic sensor signals and the bioimpedance measurements.

TECHNICAL FIELD

This disclosure relates generally to ultrasonic sensor systems andmethods for using such systems.

DESCRIPTION OF THE RELATED TECHNOLOGY

Ultrasonic fingerprint sensors have been included in devices such assmartphones, cash machines and cars to authenticate a user. A typicalultrasonic fingerprint sensor has a single function of capturingfingerprint images for user authentication. In order to provide otherfunctions, additional sensors are generally needed, which increases thecost and complexity of such systems.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosuremay be implemented in an apparatus. The apparatus may include anultrasonic sensor system and a control system that is configured forcommunication with the ultrasonic sensor system. In some examples, atleast a portion of the control system may be coupled to the ultrasonicsensor system. In some implementations, a mobile device may be, or mayinclude, the apparatus. For example, a mobile device may include anapparatus as disclosed herein. In some examples, the apparatus mayinclude a platen.

The control system may include one or more general purpose single- ormulti-chip processors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) or other programmable logic devices, discrete gates ortransistor logic, discrete hardware components, or combinations thereof.According to some examples, the control system may be configured forcontrolling the ultrasonic sensor system to transmit ultrasonic wavesand for receiving signals from the ultrasonic sensor systemcorresponding to ultrasonic waves reflected from a finger positioned onthe platen. In some examples, the control system may be configured forobtaining fingerprint image data corresponding to the signals and fordetermining a change in a force, or a result from the change in a force,of at least a portion of the finger on the platen corresponding to thesignals.

In some implementations, the control system may be configured fordetermining the change in the force according to detected changes incontact areas of fingerprint ridges on the platen. According to someexamples, wherein the control system may be configured for determiningthe change in the force according to indications of acoustic impedancechanges. The indications of acoustic impedance changes may, for example,include changes in reflection amplitudes in fingerprint ridge areas. Insome instances, the indications of increased acoustic impedance infingerprint ridge areas may include decreased reflection amplitudescorresponding with the fingerprint ridge areas. In some examples, theindications of acoustic impedance changes may be based, at least inpart, on signals R1 corresponding to reflections from aplaten/fingerprint ridge interface and on signals R2 corresponding toreflections from a platen/fingerprint valley interface. In someinstances, the indications of acoustic impedance changes may correspondto at least one of a change in a difference between R1 and R2, or achange in a sum of R1 and R2.

According to some examples, the control system may be configured fordetermining a finger action according to a detected finger forcedirection, detected changes of an overall finger force, and/or adetected rate of finger force change. The finger action may, in someinstances, include one or more low-force touches, an increasing fingertouch force, a finger tilt, a finger rotation, and/or a series ofalternating low-force and high-force finger touches. In someimplementations, the control system may be configured for controllingthe apparatus based, at least in part, on a determined finger action. Insome examples, the control system may be configured for providing atleast one of mouse functionality or joystick functionality forcontrolling the apparatus based, at least in part, on a detected fingerforce direction. According to some examples, the finger force directionmay be detected according to changes in fingerprint ridge patternscorresponding with a shear stress of fingerprint ridges in contact withthe platen.

According to some implementations, the control system may be configuredfor estimating changes in finger temperature based, at least on part, onthe signals. In some examples, the control system may be configured fordetecting changes in finger hydration status or a skin conditioncorresponding to the signals. According to some such examples, thecontrol system may be configured for detecting changes in fingerhydration status over a period of time. The changes in finger hydrationstatus may, in some examples, correspond with multiple instances ofreceiving signals from the ultrasonic sensor system.

Some or all of the operations, functions and/or methods described hereinmay be performed by one or more devices according to instructions (e.g.,software) stored on non-transitory media. Such non-transitory media mayinclude memory devices such as those described herein, including but notlimited to random access memory (RAM) devices, read-only memory (ROM)devices, etc. Accordingly, some innovative aspects of the subject matterdescribed in this disclosure can be implemented in one or morenon-transitory media having software stored thereon.

For example, the software may include instructions for controlling oneor more devices to perform a method. According to some examples, themethod may correspond to control system functionality that is disclosedherein.

In some examples, the method may involve controlling an ultrasonicsensor system to transmit ultrasonic waves and receiving signals fromthe ultrasonic sensor system corresponding to ultrasonic waves reflectedfrom a finger positioned on a platen. In some such examples, the methodmay involve obtaining fingerprint image data corresponding to thesignals and determining a change in a force, or a result from the changein a force, of at least a portion of the finger on the platencorresponding to the signals.

According to some implementations, the software may include instructionsfor determining the change in the force according to detected changes incontact areas of fingerprint ridges on the platen. In someimplementations, the software may include instructions for determiningthe change in the force according to indications of acoustic impedancechanges. In some examples, the software may include instructions fordetermining the change in the force according to indications of acousticimpedance changes. According to some examples, the indications ofacoustic impedance changes include indications of increased acousticimpedance in fingerprint ridge areas. The indications of increasedacoustic impedance in fingerprint ridge areas may include decreasedreflection amplitudes corresponding with the fingerprint ridge areas. Insome examples, the indications of acoustic impedance changes are based,at least in part, on signals R1 corresponding to reflections from aplaten/fingerprint ridge interface and on signals R2 corresponding toreflections from a platen/fingerprint valley interface.

In some implementations, the software may include instructions fordetermining a finger action and for controlling an apparatus based, atleast in part, on a determined finger action. In some examples, thesoftware may include instructions for providing at least one of mousefunctionality or joystick functionality for controlling the apparatusbased, at least in part, on a detected finger force direction. Accordingto some examples, the software may include instructions for estimatingchanges in finger temperature based, at least in part, on the signals.In some examples, the software may include instructions for detectingchanges in finger hydration status over a period of time. The changes infinger hydration status may, for example, correspond with multipleinstances of receiving signals from the ultrasonic sensor system.

Some innovative aspects of the subject matter described in thisdisclosure may be implemented in a method. The method may involvecontrolling an ultrasonic sensor system to transmit ultrasonic waves andreceiving signals from the ultrasonic sensor system corresponding toultrasonic waves reflected from a finger positioned on a platen. In someinstances, the method may involve obtaining fingerprint image datacorresponding to the signals and determining a change in a force, or aresult from the change in a force, of at least a portion of the fingeron the platen corresponding to the signals. In some implementations, themethod may involve determining the change in the force according todetected changes in contact areas of fingerprint ridges on the platen.

Some innovative aspects of the subject matter described in thisdisclosure may be implemented in a mobile device. In some examples, themobile device may include a first fingerprint sensor residing on a firstside of the mobile device. In some implementations, the firstfingerprint sensor may include a platen. According to some examples, thefirst fingerprint sensor may be, or may include, an ultrasonicfingerprint sensor. However, in alternative implementations the firstfingerprint sensor may not include an ultrasonic fingerprint sensor. Forexample, the first fingerprint sensor may include a capacitivefingerprint sensor, an optical fingerprint sensor, a thermal fingerprintsensor, a radio frequency fingerprint sensor, etc.

The mobile device may include a display residing on a second side of themobile device, the second side being opposite from the first side.According to some implementations, the mobile device may include acontrol system configured for communication with the first fingerprintsensor and the display. In some examples, the control system may beconfigured for receiving first fingerprint sensor signals from the firstfingerprint sensor corresponding to a fingerprint contact area of afirst finger positioned on the platen, for detecting one or more fingerdistortions corresponding to changes of the first fingerprint sensorsignals and for controlling the mobile device based, at least in part,on the one or more finger distortions.

According to some examples, controlling the mobile device may includeinitiating a device wake-up process, authenticating a user, unlocking adevice, selecting a menu item, starting an application, emulating aclick or a double-click, moving a cursor or pointer, interacting with abrowser application, detecting a swipe gesture, detecting a swirlgesture, operating a game, changing a brightness, changing a volume,consummating a transaction, initiating a call and/or operating a camera.In some examples, the control system may be configured for determining anavigational input corresponding with one or more finger distortions.Controlling the mobile device may involve controlling the display based,at least in part, on the navigational input.

In some implementations, the control system may be configured fordetecting a change of the fingerprint contact area and for controllingthe mobile device based, at least in part, on the detected change of thefingerprint contact area. For example, the control system may beconfigured for providing at least one of mouse functionality or joystickfunctionality for controlling the mobile device based, at least in part,on the one or more detected finger distortions or the detected change ofthe fingerprint contact area.

According to some implementations, the control system may be configuredfor detecting the one or more finger distortions according to detectedchanges in spacing between fingerprint features. For example, thedetected changes in spacing include detected changes in one or more ofridge-to-ridge spacing, valley-to-valley spacing or ridge-to-valleyspacing. In some examples, the changes in spacing may be detected in aperipheral region of the fingerprint contact area. According to someexamples, the fingerprint features may include fingerprint minutiaeand/or sweat pores. In some examples, the control system may beconfigured for detecting the one or more finger distortions according todetected changes in spacing between fingerprint features in a centralregion of the fingerprint contact area and fingerprint features in aperipheral region of the fingerprint contact area. In someimplementations, the control system may be configured for interpreting adetected change in spacing between fingerprint features as correspondingto a direction of navigational input, a magnitude of navigational input,or both a direction and a magnitude of navigational input.

In some examples, the one or more finger distortions may correspond withnon-sliding movements of the first finger while the first finger is incontact with the platen. However, in some instances the one or morefinger distortions may correspond with sliding movements of the firstfinger while the first finger is in contact with the platen.

According to some examples, detecting one or more finger distortions mayinvolve detecting a rotational movement of the first finger and thecontrol system may be configured for controlling the mobile devicebased, at least in part, on the rotational movement. In some examples,detecting a rotational movement of the first finger may involvedetecting a finger rotation direction and/or a finger rotation magnitudeof the first finger. In some such examples, the control system may beconfigured for controlling the mobile device based, at least in part, onthe finger rotation direction and/or the finger rotation magnitude.

In some implementations, the mobile device may include a secondfingerprint sensor residing on the second side of the mobile device. Thecontrol system may be configured for communication with the secondfingerprint sensor. According to some such implementations, the controlsystem may be further configured for receiving second fingerprint sensorsignals from the second fingerprint sensor corresponding to a secondfinger positioned on the second fingerprint sensor. In some examples,the control system may be further configured for detecting one or morefinger distortions of the second finger corresponding to changes of thesecond fingerprint sensor signals and controlling the mobile devicebased, at least in part, on the one or more finger distortions of thesecond finger. In some instances, the first finger or the second fingermay be a thumb. In some examples, the control system may be furtherconfigured for performing an authentication process that is based, atleast in part, on the first fingerprint sensor signals and the secondfingerprint sensor signals.

Innovative aspects of the subject matter described in this disclosurecan be implemented in one or more non-transitory media having softwarestored thereon. In some examples, the software may include instructionsfor receiving first fingerprint sensor signals from a first fingerprintsensor residing on a first side of a mobile device. The mobile devicemay have a display residing on a second side of the mobile device. Thesecond side may be opposite from the first side. The first fingerprintsensor may include a platen. The first fingerprint sensor signals maycorrespond to a fingerprint contact area of a first finger positioned onthe platen. In some implementations, the software may includeinstructions for detecting one or more finger distortions correspondingto changes of the first fingerprint sensor signals and for controllingthe mobile device based, at least in part, on the one or more fingerdistortions.

According to some examples, controlling the mobile device may involve adevice wake-up process, authenticating a user, unlocking a device,selecting a menu item, starting an application, emulating a click or adouble-click, moving a cursor or pointer, interacting with a browserapplication, detecting a swipe gesture, detecting a swirl gesture,operating a game, changing a brightness, changing a volume, consummatinga transaction, initiating a call and/or operating a camera.

In some implementations, the software may include instructions fordetermining a navigational input corresponding with one or more fingerdistortions. In some such implementations, controlling the mobile devicemay involve controlling the display based, at least in part, on thenavigational input.

According to some examples, the software may include instructions fordetecting the one or more finger distortions according to detectedchanges in spacing between fingerprint features. In someimplementations, detecting one or more finger distortions may involvedetecting a rotational movement of the first finger. In some suchimplementations, the software may include instructions for controllingthe mobile device based, at least in part, on the rotational movement.

According to some implementations, the software may include instructionsfor receiving second fingerprint sensor signals from a secondfingerprint sensor residing on a second side of the mobile device. Thesecond fingerprint sensor signals may correspond to a second fingerpositioned on the second fingerprint sensor. In some implementations,the software may include instructions for performing an authenticationprocess that is based, at least in part, on the first fingerprint sensorsignals and the second fingerprint sensor signals.

Some innovative aspects of the subject matter described in thisdisclosure may be implemented in a method of controlling a mobiledevice. The method may involve receiving first fingerprint sensorsignals from a first fingerprint sensor residing on a first side of themobile device. The mobile device may have a display residing on a secondside of the mobile device. The second side may be opposite from thefirst side. The first fingerprint sensor may include a platen. The firstfingerprint sensor signals may correspond to a fingerprint contact areaof a first finger positioned on the platen. In some implementations, themethod may involve detecting one or more finger distortionscorresponding to changes of the first fingerprint sensor signals andcontrolling the mobile device based, at least in part, on the one ormore finger distortions. In some examples, the method may involvedetermining a navigational input corresponding with one or more fingerdistortions. Controlling the mobile device may involve controlling thedisplay based, at least in part, on the navigational input.

Other innovative aspects of the subject matter described in thisdisclosure may be implemented in an apparatus. The apparatus may includean ultrasonic sensor system, a set of bioimpedance electrodes and acontrol system that is configured for communication with the ultrasonicsensor system and the set of bioimpedance electrodes. In some examples,at least a portion of the control system may be coupled to theultrasonic sensor system and/or the set of bioimpedance electrodes. Insome implementations, a mobile device may be, or may include, theapparatus. For example, a mobile device may include an apparatus asdisclosed herein. In some examples, the apparatus may include a platen.In some such examples, the set of bioimpedance electrodes may resideproximate the platen.

In some examples, the control system may be configured for controllingthe ultrasonic sensor system to transmit ultrasonic waves and forreceiving ultrasonic sensor signals from the ultrasonic sensor systemcorresponding to ultrasonic waves reflected from a portion of a body incontact with the platen. In some such examples, the control system maybe configured for receiving bioimpedance measurements from the set ofbioimpedance electrodes and for estimating a status of one or morebiometric indicators of the portion of the body based on the ultrasonicsensor signals and the bioimpedance measurements.

According to some implementations, the control system may be configuredfor determining changes in at least one of capacitance or resistance ofthe portion of the body according to changes of the bioimpedancemeasurements. In some examples, the one or more biometric indicators mayinclude skin hydration level, skin oiliness level, skin dryness and/orskin elasticity. In some implementations, the control system may beconfigured to modify one or more of the bioimpedance measurementsaccording to the ultrasonic sensor signals.

According to some examples, the bioimpedance electrodes may includecapacitive sense electrodes. In some such examples, the capacitive senseelectrodes may include interdigitated capacitive sense electrodes. Insome implementations, the control system may be configured foractivating a first subset of the capacitive sense electrodes with one ormore sensor excitation frequencies and for receiving an electricalresponse from a second subset of the capacitive sense electrodes. Theelectrical response may, for example, include an output signalamplitude, a phase delay, or both an output signal amplitude and a phasedelay. According to some implementations, estimating the status of theone or more biometric indicators may involve determining an effectivedielectric permittivity of the portion of the body and comparing theeffective dielectric permittivity with a reference dielectricpermittivity. In some examples, the control system may be configured foractivating the first subset of the capacitive sense electrodes with aplurality of sensor excitation frequencies and for determining aplurality of effective dielectric permittivities of the portion of thebody. Each of the plurality of effective dielectric permittivities maycorrespond to a sensor excitation frequency of the plurality of sensorexcitation frequencies. In some such examples, the control system may beconfigured for comparing the effective dielectric permittivities withreference dielectric permittivities.

In some implementations, the control system may be configured forcalculating, based on the ultrasonic sensor signals, one or moreacoustic impedance values for the portion of the body. In some suchimplementations, the control system may be configured for estimating thestatus of the one or more biometric indicators based on the one or moreacoustic impedance values and the bioimpedance measurements. In someexamples, the control system may be configured for calculating acomposite measurement based on the one or more acoustic impedance valuesand the bioimpedance measurements, and for determining a skin conditionof the portion of the body based, at least in part, on the compositemeasurement.

In some examples, the apparatus may include a substrate. According tosome such examples, the set of bioimpedance electrodes may reside on thesubstrate. According to some examples, ultrasonic sensors of theultrasonic sensor system also may reside on the substrate.

In some instances, the portion of the body may be a finger. According tosome such examples, the control system may be configured to determine,based on the ultrasonic sensor signals, a fingerprint contact area. Insome such examples, estimating the status of one or more biometricindicators may be based, at least in part, on the fingerprint contactarea. According to some examples, the apparatus may include a userinterface system. The control system may be configured to providefeedback, via the user interface system, regarding the fingerprintcontact area.

According to some implementations, the control system may be configuredfor determining a liveness indicator based, at least in part, on thebioimpedance measurements. In some such implementations, the controlsystem may be configured for performing an authentication process based,at least in part, on the ultrasonic sensor signals and the livenessindicator.

In some examples, the authentication process may also be based on abiometric indicator. The control system may be configured for generatingthe biometric indicator from the bioimpedance measurements. In some suchimplementations, the authentication process may involve determiningwhether the biometric indicator is above a predetermined lower biometricthreshold, determining whether the biometric indicator is below apredetermined upper biometric threshold, and/or determining whether thebiometric indicator is within a predetermined biometric range.

According to some implementations, the authentication process mayinvolve determining current fingerprint data based on the ultrasonicsensor signals, modifying the current fingerprint data according to thebioimpedance measurements, to produce modified current fingerprint data,and comparing the modified current fingerprint data with storedfingerprint data of an enrolled user. In some such implementations,modifying the current fingerprint data may involve a ridge-flowcorrection, a dry-finger correction, a wet-finger correction and/or anoily-finger correction.

In some implementations, the authentication process may involvedetermining current fingerprint data based on the ultrasonic sensorsignals and adjusting a fingerprint matching process according to thebioimpedance measurements. In some such implementations, theauthentication process may involve comparing, according to the adjustedfingerprint matching process, the current fingerprint data with storedfingerprint data of an enrolled user.

According to some examples, the control system may be configured forcontrolling the ultrasonic sensor system to obtain three-dimensionalimage data and for extracting acoustic information from the bioimpedancemeasurements. According to some such examples, the control system may beconfigured for modifying the three-dimensional image data according tothe acoustic information.

Innovative aspects of the subject matter described in this disclosuremay be implemented in a method. The method may involve controlling anultrasonic sensor system to transmit ultrasonic waves and receivingultrasonic sensor signals from the ultrasonic sensor systemcorresponding to ultrasonic waves reflected from a portion of a body. Insome implementations, the method may involve receiving bioimpedancemeasurements from a set of bioimpedance electrodes and estimating astatus of one or more biometric indicators of the portion of the bodybased on the ultrasonic sensor signals and the bioimpedancemeasurements. According to some examples, the one or more biometricindicators may include at least one biometric indicator selected from alist of biometric indicators consisting of skin hydration level, skinoiliness level, skin dryness and skin elasticity.

In some implementations, the bioimpedance electrodes may includecapacitive sense electrodes. In some such implementations, the methodmay involve activating a first subset of the capacitive sense electrodeswith one or more sensor excitation frequencies and receiving anelectrical response from a second subset of the capacitive senseelectrodes.

Innovative aspects of the subject matter described in this disclosuremay be implemented in a non-transitory medium having software storedthereon. According to some examples, the software may includeinstructions for controlling an ultrasonic sensor system to transmitultrasonic waves and for receiving ultrasonic sensor signals from theultrasonic sensor system corresponding to ultrasonic waves reflectedfrom a portion of a body. In some examples, the software may includeinstructions for receiving bioimpedance measurements from a set ofbioimpedance electrodes and for estimating a status of one or morebiometric indicators of the portion of the body based on the ultrasonicsensor signals and the bioimpedance measurements.

In some examples, the software may include instructions for determininga liveness indicator based, at least in part, on the bioimpedancemeasurements. In some such examples, the software may includeinstructions for performing an authentication process based, at least inpart, on the ultrasonic sensor signals and the liveness indicator.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale. Like reference numbers and designations in the various drawingsindicate like elements.

FIG. 1 is a block diagram that shows example components of an apparatusaccording to some disclosed implementations.

FIG. 2 is a flow diagram that provides example blocks of some methodsdisclosed herein.

FIGS. 3A and 3B are images that correspond with signals provided by anultrasonic fingerprint sensor for a light finger touch and a heavyfinger touch, respectively.

FIGS. 4A and 4B depict a portion of a finger being pressed with a lightforce and a heavy force, respectively, against a smooth platen.

FIGS. 4C and 4D show the portion of the finger being pressed with alight force and a heavy force, respectively, against a relatively roughplaten.

FIG. 5 shows an example of a cross-sectional view of an apparatuscapable of performing at least some methods that are described herein.

FIGS. 6A and 6B show examples of a mobile device that is configured forproviding mouse functionality and/or joystick functionality.

FIGS. 7A and 7B are images that represent fingerprint image datacorresponding to upwards and downwards finger forces, respectively.

FIGS. 8A and 8B show additional examples of a mobile device that isconfigured for providing mouse functionality and/or joystickfunctionality.

FIGS. 9A and 9B are images that represent fingerprint image datacorresponding to lateral (e.g., left- and right-directed) finger forces.

FIG. 10A illustrates an example of a mobile display device with afingerprint.

FIG. 10B illustrates a tip of a finger positioned on an outer surface ofthe fingerprint sensor.

FIG. 11 shows illustrative images that represent translational movementsof a finger on a platen of a fingerprint sensor and correspondingnavigational inputs.

FIG. 12 shows illustrative images representing exertions of a fingerthat generate shear forces on a platen of a fingerprint sensor andcorresponding navigational inputs.

FIG. 13 shows illustrative images that represent compressions andexpansions of fingerprint ridge spacings resulting from shear forcesgenerated by exertions of a finger on a platen of a fingerprint sensorand corresponding navigational inputs.

FIG. 14 shows illustrative images that represent movement of afingerprint contact area with respect to one or more fingerprintfeatures resulting from shear forces generated by exertions of a fingeron a platen of a fingerprint sensor and corresponding navigationalinputs.

FIG. 15 shows illustrative images that represent rotational movement ofa fingerprint contact area with respect to one or more fingerprintfeatures resulting from torsional forces generated by exertions of afinger on a platen of a fingerprint sensor and correspondingnavigational inputs.

FIG. 16 shows illustrative images that represent changing fingerprintcontact area with respect to one or more fingerprint features resultingfrom changing normal forces generated by exertions of a finger on aplaten of a fingerprint sensor and corresponding navigational inputs.

FIG. 17 shows representative sequences of forces and motions of a fingerpositioned on a platen of a fingerprint sensor that may be translatedinto predetermined commands for initiating and performing variousfunctions.

FIG. 18 illustrates an augmented ultrasonic sensor array of anultrasonic sensor system that includes one or more capacitive senseelectrodes and temperature sensing devices for detecting fingerposition, finger proximity, finger hydration, finger temperature and/orfinger motion.

FIG. 19 representationally depicts aspects of a 4×4 pixel array ofsensor pixels for an ultrasonic sensor system.

FIGS. 20A and 20B show example arrangements of ultrasonic transmittersand receivers in an ultrasonic sensor system, with other arrangementsbeing possible.

FIG. 20C shows an example of an ultrasonic transceiver array in anultrasonic sensor system.

FIG. 21 shows examples of multiple acquisition time delays beingselected to receive acoustic waves reflected from different depths.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein may be applied in a multitude ofdifferent ways. The described implementations may be implemented in anydevice, apparatus, or system that includes a biometric system asdisclosed herein. In addition, it is contemplated that the describedimplementations may be included in or associated with a variety ofelectronic devices such as, but not limited to: mobile telephones,multimedia Internet enabled cellular telephones, mobile televisionreceivers, wireless devices, smartphones, smart cards, wearable devicessuch as bracelets, armbands, wristbands, rings, headbands, patches,etc., Bluetooth® devices, personal data assistants (PDAs), wirelesselectronic mail receivers, hand-held or portable computers, netbooks,notebooks, smartbooks, tablets, printers, copiers, scanners, facsimiledevices, global positioning system (GPS) receivers/navigators, cameras,digital media players (such as MP3 players), camcorders, game consoles,wrist watches, clocks, calculators, television monitors, flat paneldisplays, electronic reading devices (e.g., e-readers), mobile healthdevices, computer monitors, auto displays (including odometer andspeedometer displays, etc.), cockpit controls and/or displays, cameraview displays (such as the display of a rear view camera in a vehicle),electronic photographs, electronic billboards or signs, projectors,architectural structures, microwaves, refrigerators, stereo systems,cassette recorders or players, DVD players, CD players, VCRs, radios,portable memory chips, washers, dryers, washer/dryers, automatic tellermachines (ATMs), parking meters, packaging (such as in electromechanicalsystems (EMS) applications including microelectromechanical systems(MEMS) applications, as well as non-EMS applications), aestheticstructures (such as display of images on a piece of jewelry or clothing)and a variety of EMS devices. The teachings herein also may be used inapplications such as, but not limited to, electronic switching devices,radio frequency filters, sensors, accelerometers, gyroscopes,motion-sensing devices, magnetometers, inertial components for consumerelectronics, parts of consumer electronics products, automobile doors,steering wheels or other automobile parts, varactors, liquid crystaldevices, electrophoretic devices, drive schemes, manufacturing processesand electronic test equipment. Thus, the teachings are not intended tobe limited to the implementations depicted solely in the Figures, butinstead have wide applicability as will be readily apparent to onehaving ordinary skill in the art.

In some implementations, an apparatus may include a multi-functionalultrasonic sensor system and a control system configured not only forfingerprint sensing, but also for detecting changes in position or force(such as changes in normal force or shear force), e.g., when a finger ispushed, pressed or slid against a platen or another surface. In someimplementations, the control system may be capable of determining aposition or a change in position of a finger on a platen by determiningthe position or change in position of one or more fingerprint features(e.g., keypoints or fingerprint minutiae) of the finger with respect tothe platen. In some examples, the position or change in position of thefinger may be determined by determining the position of one or morefingerprint features with respect to the edge of the fingerprint regionthat is in contact with the platen as the finger is pressed or slidagainst the platen. In some implementations, the control system may becapable of determining changes in force according to detected changes incontact area of one or more fingerprint ridges on the platen. In someexamples, changes in force may be determined by comparing the contactedarea of fingerprint ridges on the platen to the non-contacted area offingerprint valleys between the ridges within the fingerprint region,such as by calculating a ratio of ridge area to the total area of thefingerprint region, a ratio of valley area to the total area of thefingerprint region, or a ratio of ridge area to valley area in thefingerprint region. According to some examples, the control system maybe capable of determining changes in force according to indications ofacoustic impedance changes, such as indications of increased ordecreased acoustic impedance in fingerprint ridge areas. Indications ofincreased or decreased acoustic impedances in the fingerprint ridgeareas may be determined from measurements of the amplitude of thereflected ultrasonic wave from the platen surface by the ultrasonicsensor array. According to some implementations, the control system maybe configured to detect changes in a normal force or a shear forcedistribution of a finger pressing and/or sliding against a platensurface by detecting localized changes in one or more ridge-to-ridgespacings due to finger pressure or a finger sliding on the platensurface, particularly near the edges of the fingerprint region, and/orthe difference in acoustic impedance in the fingerprint ridge areas.Shear forces in the fingerprint region may be created or changed with orwithout a finger actually sliding along the platen surface. For example,shear forces may cause an increase in a ridge-to-ridge spacing near theleading edge of the fingerprint region and/or a decrease in aridge-to-ridge spacing near the trailing edge of the fingerprint region.

According to some implementations, the control system may be configuredfor determining a finger action according to a detected position, changein a position, rate of change of a position, and/or direction of changeof the position of a finger on the platen. According to someimplementations, the control system may be configured for determining afinger action according to a detected finger force (such as a detectednormal or shear force), finger force direction, change of an overallfinger force magnitude, change in a finger force direction, rate offinger force change, and/or rate of change of a finger force direction.According to some implementations, the control system may be configuredfor determining a finger action according to a number of taps and/ortiming of tapping a finger against a platen surface; a number ofinstances and/or timing of increasing force/pressure and decreasingforce/pressure of a finger that remains in physical contact with theplaten surface; a number of instances, timing and/or a direction ofgenerating and releasing shear force from a finger sliding along orremaining in contact with the platen surface; and/or a rate, timing anddirection of twist of a finger in contact with the platen surface. Insome implementations, the determined finger action may initiate, selector modify a function or an application running on a mobile device.According to some implementations, the control system may be configuredfor determining a finger action by detecting both a finger position anda finger force or changes to the finger position and/or force of afinger on the platen.

Particular implementations of the subject matter described in thisdisclosure may be implemented to realize one or more of the followingpotential advantages. Detected finger actions may, in some examples,correspond with various types of user input. For example, a sustained“hard press” (e.g. high force) finger action may correspond with userinput indicating that a transaction should be confirmed. A brief “lightpress” (e.g. low force) finger action may, in some instances, correspondwith user input for previewing a message before opening it. A brief,high normal force of a finger pressing against a platen surface maycorrespond to an action that makes a selection. A low, sustained normalforce of a finger may correspond to an action that scrolls through amenu. A low shear force from a finger pressing sideways (sliding orstationary) on a platen surface may correspond to an action that moves acursor, pointer or selection icon sideways depending on the direction ofthe shear force. A high shear force from a finger pressing sideways maycorrespond to an action that moves a cursor, pointer or selection iconsideways in the corresponding direction at a faster rate. An upwards ordownwards motion of a finger pressing on the platen surface maycorrespond to movements of a cursor, pointer or selection icon upwardsor downwards on a display device depending on the magnitude and/ordirection of the shear force. A rotational motion of a finger on theplaten surface (sliding or not sliding) may correspond to a desire torotate an image on the display device clockwise or counterclockwise to alandscape or portrait view or to perform another function. A zoom-in orzoom-out function may correspond to a clockwise or counter-clockwisetorque applied by the finger against the platen. Note that these actionsmay be performed without the use of a touchscreen on a display device orwithout an external mouse, scroll wheel, trackpoint or trackball. Theseactions may be performed with a multi-functional fingerprint sensormounted on the front side, backside or sidewall of a mobile deviceenclosure. In some implementations with a multi-functional fingerprintsensor mounted on the backside of a mobile device enclosure, a secondfingerprint sensor may be mounted on the front side of the sameenclosure.

Additional information, such as the time duration of pressing, a numberof “clicks” or pressings of a finger, or a time interval betweenpressings (normal and/or shear) on a platen surface may be used to allowmore types of user actions to be detected. In some examples, the controlsystem may be configured for controlling the apparatus based, at leastin part, on a determined finger action. In some such examples, thecontrol system may be configured for providing at least one of mousefunctionality or joystick functionality for controlling the apparatusbased, at least in part, on a detected finger force magnitude, directionand/or sequence, which may be conducted through direct detection offorce or through a secondary effect resulting from such force, such asthe relative strength of ultrasonic reflections from fingerprint valleysand ridges, the relative position of such stronger or weakerreflections, or the distance between such reflections.

In some examples, the ultrasonic fingerprint sensor may be able todetect changes in skin temperature and/or changes in skin hydrationstatus (such as monitoring indications of dehydration of the user). Insome examples, the ultrasonic fingerprint sensor may be augmented withone or more detection electrodes to aid in further determining skinoiliness, skin hydration or a skin condition. Accordingly, in someimplementations an ultrasonic fingerprint sensor can providemulti-functional sensor capabilities.

FIG. 1 is a block diagram that shows example components of an apparatusaccording to some disclosed implementations. In this example, theapparatus 101 includes an ultrasonic sensor system 102, a control system106 and a platen 110. Some implementations of the apparatus 101 mayinclude an interface system 104.

In some examples, as suggested by the dashed lines within the ultrasonicsensor system 102, the ultrasonic sensor system 102 may include anultrasonic sensor array 103 and a separate ultrasonic transmitter 105.In some such examples, the ultrasonic transmitter 105 may include anultrasonic plane-wave generator, such as those described below.

However, various examples of ultrasonic sensor systems 102 are disclosedherein, some of which may include a separate ultrasonic transmitter 105and some of which may not. Although shown as separate elements in FIG.1, in some implementations the ultrasonic sensor array 103 and theultrasonic transmitter 105 may be combined in an ultrasonic transceiversystem. For example, in some implementations, the ultrasonic sensorsystem 102 may include a piezoelectric receiver layer, such as a layerof PVDF polymer or a layer of PVDF-TrFE copolymer. In someimplementations, a separate piezoelectric layer may serve as theultrasonic transmitter. In some implementations, a single piezoelectriclayer may serve as both a transmitter and a receiver. In someimplementations that include a piezoelectric layer, other piezoelectricmaterials may be used in the piezoelectric layer, such as aluminumnitride (AlN) or lead zirconate titanate (PZT). The ultrasonic sensorsystem 102 may, in some examples, include an array of ultrasonictransducer elements, such as an array of piezoelectric micromachinedultrasonic transducers (PMUTs), an array of capacitive micromachinedultrasonic transducers (CMUTs), etc. In some such examples, PMUTelements in a single-layer array of PMUTs or CMUT elements in asingle-layer array of CMUTs may be used as ultrasonic transmitters aswell as ultrasonic receivers.

The control system 106 may include one or more general purpose single-or multi-chip processors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) or other programmable logic devices, discrete gates ortransistor logic, discrete hardware components, or combinations thereof.The control system 106 also may include (and/or be configured forcommunication with) one or more memory devices, such as one or morerandom access memory (RAM) devices, read-only memory (ROM) devices, etc.Accordingly, the apparatus 101 may have a memory system that includesone or more memory devices, though the memory system is not shown inFIG. 1. The control system 106 may be capable of receiving andprocessing data from the ultrasonic sensor system 102, e.g., from theultrasonic sensor array 103. If the apparatus 101 includes a separateultrasonic transmitter 105, the control system 106 may be capable ofcontrolling the ultrasonic transmitter 105, e.g., as disclosed elsewhereherein. In some implementations, functionality of the control system 106may be partitioned between one or more controllers or processors, suchas between a dedicated sensor controller and an applications processorof a mobile device.

Some implementations of the apparatus 101 may include an interfacesystem 104. In some examples, the interface system may include awireless interface system. In some implementations, the interface systemmay include a user interface system, one or more network interfaces, oneor more interfaces between the control system 106 and a memory system,and/or one or more interfaces between the control system 106 and one ormore external device interfaces (e.g., ports or applicationsprocessors).

The interface system 104 may be configured to provide communication(which may include wired or wireless communication, such as electricalcommunication, radio communication, etc.) between components of theapparatus 101. In some such examples, the interface system 104 may beconfigured to provide communication between the control system 106 andthe ultrasonic sensor system 102. According to some such examples, aportion of the interface system 104 may couple at least a portion of thecontrol system 106 to the ultrasonic sensor system 102, e.g., viaelectrically conducting material. If the apparatus 101 includes anultrasonic transmitter 105 that is separate from the ultrasonic sensorarray 103, the interface system 104 may be configured to providecommunication between at least a portion of the control system 106 andthe ultrasonic transmitter 105. According to some examples, theinterface system 104 may be configured to provide communication betweenthe apparatus 101 and other devices and/or human beings. In some suchexamples, the interface system 104 may include one or more userinterfaces. The interface system 104 may, in some examples, include oneor more network interfaces and/or one or more external device interfaces(such as one or more universal serial bus (USB) interfaces or a systempacket interface (SPI)). In some implementations, the apparatus 101 mayinclude a memory system. The interface system 104 may, in some examples,include at least one interface between the control system 106 and amemory system.

The apparatus 101 may be used in a variety of different contexts, someexamples of which are disclosed herein. For example, in someimplementations a mobile device may include at least a portion of theapparatus 101. In some implementations, a wearable device may include atleast a portion of the apparatus 101. The wearable device may, forexample, be a bracelet, an armband, a wristband, a ring, a headband or apatch. In some implementations, the control system 106 may reside inmore than one device. For example, a portion of the control system 106may reside in a wearable device and another portion of the controlsystem 106 may reside in another device, such as a mobile device (e.g.,a smartphone). The interface system 104 also may, in some such examples,reside in more than one device.

FIG. 2 is a flow diagram that provides example blocks of some methodsdisclosed herein. The blocks of FIG. 2 (and those of other flow diagramsprovided herein) may, for example, be performed by the apparatus 101 ofFIG. 1 or by a similar apparatus. As with other methods disclosedherein, the method outlined in FIG. 2 may include more or fewer blocksthan indicated. Moreover, the blocks of methods disclosed herein are notnecessarily performed in the order indicated.

In this example, block 203 involves controlling an ultrasonic sensorsystem, such as the ultrasonic sensor system 102 of FIG. 1, to transmitultrasonic waves. According to this implementation, block 205 involvesreceiving signals from the ultrasonic sensor system corresponding toultrasonic waves reflected from a finger positioned on a platen. In someexamples, block 205 may involve receiving signals from the ultrasonicsensor system corresponding to ultrasonic waves reflected from anothertype of target object positioned on a platen.

According to this example, block 207 involves obtaining fingerprintimage data corresponding to the signals. As used herein, the term“fingerprint image data” may refer generally to data obtained from, ordata based on signals obtained from, a target object such as a fingerthat may include a fingerprint. The fingerprint image data may or maynot be presented in a form that is recognizable to a human being asbeing an image. For example, the fingerprint image data may be, or mayinclude, a data structure in which numerical values are arranged and/orstored. The numerical values may, in some examples, correspond tosignals received from an ultrasonic sensor system, an optical sensorsystem, a capacitive sensor system, etc. In some examples, thefingerprint image data may correspond to signals received from a sensorsystem during a time window. In some instances, the fingerprint imagedata may correspond to signals received from a particular area, such asa fingerprint contact area. Examples of fingerprint contact areas aredescribed below. In some instances, the fingerprint image data may be,or may include, data that has been aggregated and/or processed in somemanner after having been acquired from a sensor system. In someexamples, the fingerprint image data may include indications of one ormore fingerprint features detected in at least a portion of the signalsfrom the sensor system (such as an ultrasonic sensor system). Thefingerprint features may include one or more fingerprint ridge featuresand one or more fingerprint valley features. The fingerprint featuresmay, for example, be detected by a control system such as the controlsystem 106 of FIG. 1.

Signals indicating fingerprint ridge features may generally be obtainedfrom sensor pixels of the ultrasonic sensor system that are respondingto ultrasonic waves that have been reflected from platen/fingerprintridge interfaces. Signals indicating fingerprint valley features maygenerally be obtained from sensor pixels that are responding toultrasonic waves that have been reflected from platen/fingerprint valleyinterfaces. The reflections from a platen/fingerprint valley interfacewill generally be reflections from a platen/air interface, whereas thereflections from a platen/fingerprint ridge interface will generally bereflections from a platen/skin interface, corresponding to areas inwhich fingerprint ridges are in contact with a platen.

In various examples disclosed herein, R1 represents an amplitude of areflected ultrasonic wave from a platen/fingerprint ridge interface andR2 represents an amplitude of a reflected ultrasonic wave from aplaten/fingerprint valley interface. The amplitude R1 may be expressedas follows:

$\begin{matrix}{{R\; 1} = \frac{\left( {{Zskin} - {Zplaten}} \right)}{\left( {{Zskin} + {Zplaten}} \right)}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

In Equation 1, Z_(skin) represents the acoustic impedance of skin andZ_(platen) represents the acoustic impedance of a platen. A typicalacoustic impedance of skin is about 1.8 MRayl. A glass platen wouldtypically have an acoustic impedance of about 13.7 MRayl and an aluminumplaten would typically have an acoustic impedance of about 16.9 MRayl.Assuming that a reflection from a platen/fingerprint valley interface isa reflection from a platen/air interface, the amplitude R2 may beexpressed as follows:

$\begin{matrix}{{R\; 2} = \frac{\left( {{Zair} - {Zplaten}} \right)}{\left( {{Zair} + {Zplaten}} \right)}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In Equation 2, Z_(air) represents the acoustic impedance of air. Atypical acoustic impedance of air is about 0.00043 MRayl.

In view of the foregoing equations and acoustic impedance values, it isclear that a platen/air interface will generally provide ahigher-amplitude reflection (corresponding with R2) than aplaten/fingerprint ridge interface (corresponding with R1). Therefore,fingerprint valley features will generally correspond to regions ofrelatively high-amplitude signals and fingerprint ridge features willgenerally correspond to regions of relatively low-amplitude signals.Fingerprint valley features may, for example, correspond with continuousor piecewise-continuous regions of relatively high-amplitude signals andfingerprint ridge features may correspond with continuous orpiecewise-continuous regions of relatively low-amplitude signals. Thecontinuous or piecewise-continuous regions may correspond to lines havevarying degrees of curvature. For example, a relatively straight ridgeor valley may have a small curvature and a highly curved ridge orvalley, such as those in a fingerprint whorl region, may have a highcurvature.

In some examples the fingerprint ridge and valley features may includepattern information and/or fingerprint minutiae such as ridge endinginformation, ridge bifurcation information, short ridge information,ridge flow information, island information, spur information, deltainformation, core information, etc. Accordingly, in some instances thefingerprint features may be suitable for performing an authenticationprocess. In some implementations, a control system (such as the controlsystem 106 of FIG. 1) may be capable of initiating an authenticationprocess that is based, at least in part, on the fingerprint features. Insome implementations, the control system may be capable of performing anauthentication process that is based, at least in part, on thefingerprint features.

In this example, block 209 involves determining a change in a force(such as a change in normal or shear force) of at least a portion of thefinger on the platen corresponding to the signals. Various examples aredisclosed herein. Several phenomena allow changes in applied fingerforce to be detected by analyzing signals provided by an ultrasonicfingerprint sensor. One phenomenon is that when a finger (or anotherbody part) is pressed relatively harder against a platen, the area incontact with the platen changes. For example, the widths of the ridgeregions in contact with the platen may increase and the widths of thevalley regions between the ridge regions may decrease. Some examples ofthis phenomenon are shown in FIGS. 3A-4D.

FIGS. 3A and 3B are images that correspond with signals provided by anultrasonic fingerprint sensor for a light finger touch and a heavyfinger touch, respectively. In FIGS. 3A and 3B, the dark areas are areasof relatively low-amplitude signals that correspond with reflectionsfrom platen/fingerprint ridge interfaces (corresponding with R1).Accordingly, the dark areas are examples of fingerprint ridge features,corresponding to areas in which fingerprint ridges are in contact with aplaten of the ultrasonic fingerprint sensor. The light areas in FIGS. 3Aand 3B are areas of relatively high-amplitude signals that correspondwith reflections from a platen/air interface (corresponding with R2).The light areas that are interposed between the fingerprint ridgefeatures in FIGS. 3A and 3B are examples of fingerprint valley features.

FIG. 3A is a graphic representation of signals provided by an ultrasonicfingerprint sensor when a finger is pressing on a platen with arelatively smaller force, whereas FIG. 3B is a graphic representation ofsignals provided by the ultrasonic fingerprint sensor when the samefinger is pressing on the platen with a relatively larger force. It maybe observed that the fingerprint ridge features in FIG. 3B are darkerthan the fingerprint ridge features in FIG. 3A. Moreover, it may be seenthat the fingerprint ridge features in FIG. 3B are relatively thickerthan the fingerprint ridge features in FIG. 3A, and that the fingerprintvalley features in FIG. 3B are relatively thinner than the fingerprintvalley features in FIG. 3A.

Accordingly, the fingerprint ridge features in FIG. 3B occupy arelatively larger percentage of the platen surface than the fingerprintridge features in FIG. 3A. Because the fingerprint ridge featurescorrespond to areas of relatively lower-amplitude signals, a relativelylarger percentage of the reflections received by the ultrasonicfingerprint sensor will produce relatively lower-amplitude signals(corresponding with R1) when a finger is pressing on the platen with arelatively larger force. Accordingly, the median amplitude of signalsprovided by the ultrasonic fingerprint sensor will decrease when afinger is pressing on the platen with a relatively larger force. Anotherway of expressing this condition is that a sum (or average) of thereflected signals R1 and R2 from the platen-finger interface willdecrease when a finger is pressing on the platen with a relativelylarger force. In some implementations, a bounding box (e.g. a fingeroutline) may be determined to delineate the portion of a finger that isin contact with the platen and to define a fingerprint region that iswithin the bounding box (e.g., a region having fingerprint features) anda non-fingerprint region that is external to the bounding box (e.g., aregion having no fingerprint features). Subsequently, the reflectedsignals from sensor pixels within the fingerprint region may be used todetermine an indication of the amount of force applied by the finger bycomparing the area of the fingerprint ridges to the area of thefingerprint valleys, determining a ratio of ridge area to the area ofthe fingerprint region, or alternatively, by adding all of the signalswithin the bounding box (or in some examples throughout the entireactive area of the sensor) to determine a measure of the applied force.

The images shown in FIGS. 3A and 3B were obtained by an ultrasonicfingerprint sensor having a relatively smooth platen, as illustrated inFIGS. 4A and 4B wherein a portion of a finger is pressed with a lightforce and a heavy force, respectively, against a smooth platen. A lightpress presents relatively less ridge area and more valley area againstan outer surface of the platen as shown in FIG. 4A, compared to a hardpress that presents more ridge area and less valley area against theouter surface of the platen as shown in FIG. 4B. The above-describedeffects can be enhanced when the surface of the platen of an ultrasonicfingerprint sensor is at least slightly rough. FIGS. 4C and 4D show theportion of the finger being pressed with a light force and a heavyforce, respectively, against a relatively rough platen. As a result ofpressing harder, fingerprint ridges may deform to fill small gaps andvalleys between the platen and the finger. Accordingly, the contact areaof the “heavy force” example may increase relative to the “light force”example, for either rough or smooth platens. In some implementations, arough or moderately rough platen may represent a ground yet unpolishedaluminum or metal platen. In some implementations, a rough or moderatelyrough platen may represent a matte or textured finish of a glass orplastic cover lens of a display device.

Therefore, in some implementations block 209 of FIG. 2 may involvedetermining a change in the force of at least a portion of a finger on aplaten according to detected changes in contact areas of fingerprintridges on the platen. For example, a control system may be configuredfor determining a change in the force according to detected changes incontact areas of fingerprint ridges on the platen or in the relativechange between the aggregate ridge area and the aggregate valley areawithin the fingerprint region. In another example, the control systemmay be configured for determining a change in the finger force accordingto detected changes in the sum of the reflected signals within thefingerprint region. In another example, the control system may beconfigured for determining a change in the finger force according todetected changes in the area of one or more ridge regions. In otherexamples, the control system may be configured for determining a changein the finger force according to detected changes in the width of one ormore fingerprint ridges or an average of one or more fingerprint ridges,or alternatively according to detected changes in the width of one ormore fingerprint valleys, an average width of one or more fingerprintvalleys, or a ratio of the width of one or more fingerprint ridges tothe width of one or more fingerprint valleys.

Another phenomenon that can allow changes in applied fingerforce/pressure to be detected by an ultrasonic fingerprint sensor isthat when the finger is pressed relatively harder against the platen,the tissue in the region of a ridge becomes relatively denser, whichcorresponds to a larger value of Z_(skin). Accordingly, in someimplementations block 209 of FIG. 2 may involve determining a change inthe force of at least a portion of a finger on a platen according toindications of acoustic impedance changes.

For example, a control system may be configured for determining a changein the force of a finger that is pressed against a platen according toindications of increased acoustic impedance in fingerprint ridge areas.By reference to Equation 1, it may be seen that a relatively largervalue of Z_(skin) will result in a relatively smaller amplitude of thereflected ultrasonic waves R1, which are ultrasonic waves received fromfingerprint ridge areas. In some implementations, detecting indicationsof increased acoustic impedance in fingerprint ridge areas may involvedetecting indications that the amplitude of signals corresponding toreflections from platen/fingerprint ridge interfaces (which may bereferred to herein as “signals R1” or simply “R1”) have decreased.

In some implementations, an indication of acoustic impedance changes maybe based, at least in part, on a change in a difference between R1 andR2 or a change in a sum of R1 and R2. Some such implementations mayinvolve determining whether a delta output signal (e.g., R2−R1) hasincreased. Some examples may involve determining whether a sum of R1 andR2 (e.g., (R1+R2)/2) has decreased. In some implementations, the valueof R1 or an average value for R1 may be determined by first processingthe fingerprint images to determine one or more ridge regions, thenoperating on output signals from the one or more ridge regions.Similarly, in some implementations, the value of R2 or an average valuefor R2 may be determined by first processing the fingerprint images todetermine one or more valley regions, then operating on output signalsfrom the one or more valley regions.

In some examples, a control system may be capable of detecting changesin skin temperature according to signals from an ultrasonic sensor. Somesuch implementations may rely on the observation that the Young'smodulus of skin decreases as temperature increases. For example, as skintemperature increases from 37 to 39 degrees Centigrade, the Young'smodulus of skin may decrease by approximately 12%. As the Young'smodulus of skin decreases, the speed of sound in the skin decreases andtherefore the acoustic impedance of skin, Z_(skin), decreases. Byreference to Equation 1, it may be seen that a relatively smaller valueof Z_(skin) results in a relatively larger amplitude of the reflectedwaves R1 from a platen/fingerprint ridge interface.

Moreover, the gradient of the received signals and the speed at whichequilibrium is reached after a finger is placed on a platen of anultrasonic fingerprint sensor can indicate differences in skintemperature. For example, the higher the skin temperature, the fasterthat equilibrium may be reached. Colder fingers, as those in colderclimates know, may be slower to equilibrate.

Body temperature may be regulated through blood vessels and through theprocess of sweating. During athletic activity, sweating makes a finger(or another part of a user's body) relatively wetter. Wet skin normallyhas a smaller acoustic impedance than dry skin, due in part to theepidermal (outer) layer of skin on the finger becoming softer, the speedof sound in the softer material becoming slower, and the acousticimpedance of the wet skin lessening with increasing hydration resultingin an increase in the average output signal. However, the contact areabetween the finger and the platen increases for the same applied force,reducing the magnitude of the reflected signals in the regions ofincreased contact, reducing the average value of the reflected signals,increasing the delta (R2−R1) signals, and decreasing the average outputsignal. When considering sweat pores filling with liquid duringincreased sweating, the contact area increases, the reflected signalsdecrease in the region of the filled sweat pores, the delta (R2−R1)signals increase, and the average output signal decreases. While some ofthe factors described may partially compensate others, the outputsignal(s) from the ultrasonic sensor can provide an indicating ofhydration and sweating.

In some implementations, a control system may be capable of detectingsweat on a finger or on another part of a user's body according to inputfrom an ultrasonic sensor. In some examples, a control system may becapable of detecting changes in skin hydration status according tosignals from an ultrasonic sensor. According to some implementations, acontrol system may be capable of tracking the hydration status of auser, for example during sports and athletic activities, according toinput from an ultrasonic fingerprint sensor. In some examples, thecontrol system may be configured for detecting changes in skin hydrationstatus (e.g., of finger hydration status) over a period of time.According to some such examples, the changes in skin hydration statusmay correspond with multiple instances of receiving signals from theultrasonic sensor system.

According to some implementations, changes in a user's hydration statusmay be detected according to changes in the strength of a delta outputsignal (e.g., R2−R1). For example, in a 5-km race, a user's skin (e.g.,a finger) may stay relatively wet due to sweating. The delta signal willbe relatively smaller while the skin is wet. If the ultrasonic sensorstarts to detect a larger delta signal in one or more ridge regions,this may indicate that the sweating process is becoming limited and thatthe athlete may be entering a state of dehydration.

Some implementations may involve detecting force changes, changes in auser's temperature and/or changes in a user's hydration status based onultrasonic data obtained from parts of the body other than a portion ofa finger on which a user's fingerprint is formed. For example, a user'swrist region also includes skin features that are broadly similar tofingerprint ridges and valleys, though skin features in a user's wristregion have different geometries. Although R1 has been describedelsewhere herein as corresponding to reflections from aplaten/fingerprint ridge interface, R1 may be considered more generallyas corresponding to reflections from a platen/skin interface.

Accordingly, ultrasonic data obtained from a user's wrist may be used todetermine changes in a user's temperature and/or changes in a user'shydration status. In some such implementations, the ultrasonic data fordetermining changes in a user's temperature and/or changes in a user'shydration status may be obtained via an ultrasonic sensor system that isprovided in a wrist band, a watch, etc. In some examples, the ultrasonicdata for determining changes in a user's temperature and/or changes in auser's hydration status may be obtained via an ultrasonic sensor systemthat is provided in a skin patch, a headband, an armband, a ring, oranother wearable device.

FIG. 5 shows an example of a cross-sectional view of an ultrasonicsensor system capable of performing at least some methods that aredescribed herein. For example, the ultrasonic sensor system 102 may becapable of performing the methods that are described above, e.g., withreference to FIGS. 1 and 2. Here, the ultrasonic sensor system 102 is anexample of the ultrasonic sensor system 102 that is described above withreference to FIG. 1. As with other implementations shown and describedherein, the types of elements, the arrangement of the elements and thedimensions of the elements illustrated in FIG. 5 are merely shown by wayof example.

FIG. 5 shows an example of ultrasonic waves reflecting from a targetobject. In this example, the target object is a finger 506 beinginsonified by transmitted ultrasonic waves 514. Here, reflectedultrasonic waves 516 that are received by the ultrasonic sensor system102 include instances of R1, reflected from interfaces between theplaten 110 and fingerprint ridges, as well as instances of R2, reflectedfrom interfaces between the platen 110 and air/fingerprint valleys.

In this example, the ultrasonic sensor system includes an ultrasonictransmitter 105 that is separate from an ultrasonic sensor array 103. Inthe example shown in FIG. 5, the ultrasonic transmitter 105 can functionas a plane-wave ultrasonic transmitter. In some implementations, theultrasonic transmitter 105 may include a piezoelectric transmitter layer504 with one or more transmitter excitation electrodes 503, 505 disposedon each side of the piezoelectric transmitter layer.

In some such examples, the ultrasonic sensor array 103 may include anarray of pixel input electrodes and sensor pixels formed in part fromTFT- or silicon-based circuitry, an overlying piezoelectric receiverlayer 520 of piezoelectric material such as PVDF or PVDF-TrFE, and anupper electrode layer positioned on the piezoelectric receiver layer520, which will sometimes be referred to herein as a receiver biaselectrode 522. Examples of suitable ultrasonic transmitters andultrasonic receiver arrays are described below with reference to FIGS.20A-20C.

In alternative implementations, the ultrasonic sensor array 103 and theultrasonic transmitter 105 may be combined in an ultrasonic transceiverarray. For example, in some implementations, the ultrasonic sensorsystem may include a piezoelectric receiver layer, such as a layer ofPVDF polymer or a layer of PVDF-TrFE copolymer. In some implementations,a separate piezoelectric layer may serve as the ultrasonic transmitter.In some implementations, a single piezoelectric layer may serve as thetransmitter and as a receiver. In some implementations, otherpiezoelectric materials may be used in the piezoelectric layer, such asaluminum nitride (AlN) or lead zirconate titanate (PZT). The ultrasonicsensor system may, in some examples, include an array of ultrasonictransducer elements, such as an array of piezoelectric micromachinedultrasonic transducers (PMUTs), an array of capacitive micromachinedultrasonic transducers (CMUTs), etc. In some such examples, apiezoelectric receiver layer, PMUT elements in a single-layer array ofPMUTs, or CMUT elements in a single-layer array of CMUTs, may be used asultrasonic transmitters as well as ultrasonic receivers.

In this example, the transmitted ultrasonic waves 514 have beentransmitted from the ultrasonic transmitter 105 through a sensor stack515 and towards the overlying finger 506. The various layers of thesensor stack 515 may, in some examples, include one or more substratesof glass or other material (such as plastic or sapphire) that issubstantially transparent to visible light. In this example, the sensorstack 515 includes a substrate 510 to which a light source system (notshown) may be coupled, which may be a backlight of a display accordingto some implementations. In alternative implementations, a light sourcesystem may be coupled to a front light. Accordingly, in someimplementations a light source system may be configured for illuminatinga display and the target object.

In this implementation, the substrate 510 is coupled to a thin-filmtransistor (TFT) substrate 512 for the ultrasonic sensor system.According to this example, a piezoelectric receiver layer 520 overliessensor pixels 502 of the ultrasonic sensor array 103 and the platen 110overlies the piezoelectric receiver layer 520. Accordingly, in thisexample the ultrasonic sensor system 102 is capable of transmitting theultrasonic waves 514 through one or more substrates of the sensor stack515 that include the ultrasonic sensor system with substrate 512, aswell as the platen 110 that may also be viewed as a substrate. In someimplementations, sensor pixels 502 of the ultrasonic sensor array 103may be transparent, partially transparent or substantially transparent,such that the apparatus 101 may be capable of transmitting light from alight source system through elements of the ultrasonic sensor system. Insome implementations, the ultrasonic sensor system and associatedcircuitry may be formed on or in a glass, plastic or silicon substrate.However, in some implementations one or more of the substrates of theapparatus 101 may be translucent or opaque to visible light.

FIGS. 6A and 6B show examples of a mobile device that includes anultrasonic sensor system as disclosed herein. In this example, themobile device 650 is depicted as a smartphone. However, in alternativeexamples the mobile device 650 may another type of mobile device, suchas a mobile health device, a wearable device, a tablet computer, etc.

In this example, the mobile device 650 includes an instance of theapparatus 101 that is described above with reference to FIG. 1. In thisexample, the apparatus 101 is disposed, at least in part, within themobile device enclosure 655. According to this example, at least aportion of the apparatus 101 is located in the portion of the mobiledevice 650 that is shown being touched by a finger 506, whichcorresponds to the location of button 660. Accordingly, the button 660may be an ultrasonic button. In some implementations, the button 660 mayserve as a home button. In some implementations, the button 660 mayserve as an ultrasonic authenticating button, with the ability to turnon or otherwise wake up the mobile device 650 when touched or pressedand/or to authenticate or otherwise validate a user when applicationsrunning on the mobile device (such as a wake-up function) warrant such afunction.

In this implementation, the mobile device 650 may be capable ofperforming a user authentication process. For example, a control systemof the mobile device 650 may be capable of comparing attributeinformation obtained from data received via an ultrasonic sensor arrayof the apparatus 101 with stored attribute information obtained fromdata that has previously been received from an authorized user. In someexamples, the attribute information obtained from the received data andthe stored attribute information may include attribute informationcorresponding to fingerprint minutia. In some implementations, thefingerprint and/or attribute information may be stored as one or moreenrollment templates.

In some implementations, a control system of the apparatus 101 and/or ofthe mobile device 650 may be configured for determining a finger actionaccording to a detected finger position, a change in finger position, arate of change and direction of a finger position, a finger forcedirection, detected changes of an overall finger force, and/or adetected rate of finger force change. The finger action may, forexample, include one or more low-force touches, an increasing fingertouch force, a finger tilt, a finger lift, a finger rotation and/or aseries of alternating low-force and high-force finger touches. Accordingto some such examples, a control system may be configured forcontrolling an apparatus (such as the apparatus 101 and/or the mobiledevice 650) based, at least in part, on a determined finger action.

FIGS. 6A and 6B show examples of a mobile device that is configured forproviding mouse functionality and/or joystick functionality. In theseexamples, a control system of the mobile device 650 may be configuredfor providing mouse functionality and/or joystick functionality forcontrolling the mobile device 650 based, at least in part, on a detectedfinger force direction or through one or more secondary effectsresulting from such force. Examples of secondary effects resulting froma finger force include the relative strength of ultrasonic reflectionsfrom fingerprint valleys and ridges, the relative position of suchstronger or weaker reflections, or the distance between suchreflections. In the example shown in FIG. 6A, a control system isdetecting an “upward” force of the finger 506, in the direction of thearrow 605, according to changes in signals received from a fingerprintsensor 660 of the apparatus 101. One example is shown in FIG. 7A and isdescribed below. In response to detecting the upward force of the finger506, the control system may cause a display 610 of the mobile device 650to move an image of an object 615 in the direction of the arrow 620,which is parallel to the arrow 605 in this example. In someimplementations, the fingerprint sensor 660 may be, or may at least be aportion of, an ultrasonic sensor system 102 such as described elsewhereherein. However, in some implementations the fingerprint sensor 660 maybe another type of fingerprint sensor, such as an optical fingerprintsensor, a capacitive fingerprint sensor, a radio frequency fingerprintsensor, a thermal fingerprint sensor, etc.

In the example shown in FIG. 6B, a control system is detecting a“downward” force of the finger 506, in the direction of the arrow 607,according to changes in signals received from an ultrasonic sensorsystem of the apparatus 101. One example of an image corresponding tosuch signals is shown in FIG. 7B and is described below. In response todetecting the downward force of the finger 506, the control systemcauses the display 610 to move the image 615 in the direction of thearrow 622, which is parallel to the arrow 607 in this example. In someimplementations, the finger 506 in FIG. 6A and FIG. 6B may slide upwardsor downwards upon a platen surface of the apparatus 101. In otherimplementations, the finger 506 in FIG. 6A and FIG. 6B may be movedupwards or downwards on the platen surface without sliding, relying onshear forces, distortions of fingerprint ridges and valleys, and/ordisplacements of fingerprint features with respect to an edge of thefingerprint region to make the determinations.

FIGS. 7A and 7B are images that represent fingerprint image datacorresponding to upward and downward finger forces, respectively. InFIG. 7A, an upward force is indicated by the presence of fingerprintridge and valley features primarily in the upper portion of the image,whereas in FIG. 7B a downward force is indicated by the presence offingerprint ridge and valley features primarily in the lower portion ofthe image. This effect may or may not be caused by sliding the finger.In some instances, this effect may be a result of rocking the fingerforward or backward, and/or by changes in the shape of the finger due toshear stress. Such changes in the shape of a finger may be referred toherein as “finger distortions.” Accordingly, in some implementations afinger force direction may be detected according to changes infingerprint ridge patterns corresponding with a shear stress offingerprint ridges in contact with the platen. In some implementations,the speed at which a cursor or pointer may be moved on a display of themobile device may be determined from measurements of the reflectedultrasonic wave and calculations of the magnitude and direction of thefinger forces. For example, a higher measured finger force (normal forceor shear force) may result in faster movement of a cursor or pointer onthe display. Similarly, a lower measured finger force may result inslower movement of the cursor or pointer on the display.

FIGS. 8A and 8B show additional examples of a mobile device that isconfigured for providing mouse functionality and/or joystickfunctionality. As with the examples that are described above withreference to FIGS. 6A and 6B, in this implementation a control system ofthe mobile device 650 is configured for providing mouse functionalityand/or joystick functionality for controlling the mobile device 650based, at least in part, on a detected finger force direction. In theexample shown in FIG. 8A, a control system is detecting a lateral (e.g.,a sideward or shear) force of the finger 506, in the direction of thearrow 805, according to changes in signals received from a fingerprintsensor 660 of the apparatus 101. One example is shown in FIG. 9A and isdescribed below. In response to detecting the lateral force of thefinger 506, in this example the control system causes a display 610 ofthe mobile device 650 to move an image of an object 615 in the directionof the arrow 820, which is parallel to the arrow 805 in this example.

In the example shown in FIG. 8B, a control system is detecting a lateralforce of the finger 506 in the direction of the arrow 807, according tochanges in signals received from a fingerprint sensor 660 of theapparatus 101. One example of an image corresponding to such signals isshown in FIG. 9B and is described below. In response to detecting thelateral force of the finger 506, in this example the control systemcauses the display 610 to move an image of an object 615 in thedirection of the arrow 822, which is parallel to the arrow 807 in thisexample.

FIGS. 9A and 9B are images that represent fingerprint image datacorresponding to lateral (e.g., left- and right-directed) finger forces.In FIG. 9A, a rightward force is indicated by the presence of a higherconcentration of fingerprint ridge and valley features in the right sideof the image, whereas in FIG. 9B a leftward force is indicated by ahigher concentration of fingerprint ridge and valley features in theleft side of the image. This effect may or may not be caused by slidingthe finger. In some instances, this effect may be a result of rockingthe finger to the right or to the left, and/or by changes in the shapeof the finger due to shear stress, particularly near the edges of thefinger contact area.

The examples shown in FIGS. 6A, 6B, 8A and 8B involve a control systemcausing the display 610 to move a specific image in specific directions.However, in some implementations the control system may be capable ofcausing the display 610 to move any type of image in any direction.

Moreover, the control system may be capable of controlling the mobiledevice 650 to perform other functions in response to changes in signalsreceived from a fingerprint sensor of the apparatus 101. The fingerprintsensor may or may not be a component of an ultrasonic sensor system,depending on the particular implementation. In some implementations, acontrol system of the apparatus 101 and/or of the mobile device 650 maybe configured for determining a finger action according to detectedchanges of a finger force (e.g. a normal force and/or shear force), adirection of force, or a detected rate of finger force and/or directionchange. The finger action may, for example, include one or morelow-force touches, an increasing finger touch force, a finger lift, afinger tilt, a finger rotation and/or a series of alternating low-forceand high-force finger exertions.

Different finger actions and/or combinations of finger actions maycorrespond with different instructions for controlling the mobile device650 and/or controlling a software application that is being executed bya control system of the mobile device 650. For example, a detectedhard/higher-force finger press may be an instruction to confirm afinancial transaction. In some examples, a detected light/lower-forcefinger press may be an instruction to preview a message before openingit. Additional information, such as the magnitude and duration of anormal force, the magnitude, direction and duration of a shear force,the magnitude, direction and duration of an applied finger torque, thetime duration of the finger presses and/or the number of finger pressesmay be used to allow additional types of user actions to be detected andmay be interpreted as instructions for various types of functionality.

Calibration parameters for determining different finger actions and/orcombinations of finger actions on a platen of a fingerprint sensorsystem may be determined at a factory during testing and assembling ofthe ultrasonic sensor system. The calibration parameters may be based onimage information acquired from the fingerprint sensor system during aset of time-ordered scans of a finger as part of a factory calibrationprocedure. The factory-set calibration parameters for determining fingeractions may be based on the application and movement of a calibrationtest target and the calibration parameters may be stored in a memory ofthe fingerprint sensor system. In some implementations, the factory-setcalibration parameters may be pre-determined statistically from avariety of different user inputs without applying a calibrationprocedure to each individual fingerprint sensor system. In someimplementations, the factory-set calibration parameters may be updatedwith user inputs from a specific user, such as a user who has beenauthenticated to use the device containing the fingerprint sensorsystem. In some implementations, a user may be directed during anenrollment procedure to perform predefined actions such as applyingvarying levels of normal force, sliding a finger over the platen invarious directions, and exerting a finger in various directions withoutsliding the finger to generate varying levels of shear force. In someimplementations, the calibration parameters may be adaptively updated toaccommodate a particular user's finger and motion characteristics.

FIG. 10A illustrates an example of a mobile display device 1050 with afingerprint sensor. In this example, the fingerprint sensor 1060 is acomponent of the ultrasonic sensor system 102, whereas in other examplesthe fingerprint sensor 1060 may be, or may be a portion of, another typeof fingerprint sensor system, such as an optical fingerprint sensorsystem, a capacitive fingerprint sensor system, a radio frequencyfingerprint sensor system, a thermal fingerprint sensor system, etc. Theimplementation shown in FIG. 10A includes a backside-mountedmulti-functional ultrasonic fingerprint sensor 1060 for authenticationand navigation among other functions. In some implementations, thefingerprint sensor 1060 may be attached to a backside wall of thedisplay device 1050. In some implementations, the fingerprint sensor1060 may be positioned securely against an opening formed in thebackside wall of a mobile device enclosure 655. The backside-mountedfingerprint sensor 1060 allows a target object such as a finger 506 of auser to be positioned on a surface of the fingerprint sensor 1060. FIG.10B illustrates a tip of a finger 506 positioned on an outer surface ofa platen 110 of the fingerprint sensor 1060.

In many instances, a user may operate the display device 1050 with asingle hand including holding the display device 1050 withoutobstructing or otherwise obscuring the display 610 from viewing by auser. In some implementations, the user may walk, run or perform otherbodily functions without requiring the use of two hands to operate thedisplay device 1050. In some implementations, a fingerprint sensor 1060positioned on the backside of the enclosure 655 may be augmented with asecond fingerprint sensor (not shown) that is accessible from the front(e.g. display side) of the display device 1050 for increased convenienceand functionality. In some such implementations, a two-sidedauthentication process may be performed wherein a first finger of a useris authenticated using a first fingerprint sensor 1060 on the backsideof the enclosure 655 and a second finger of the user is authenticatedusing a second fingerprint sensor that is accessible from the front ofthe display device 1050, and wherein the two fingers of the user areauthenticated sequentially or simultaneously. As used herein, the term“finger” can refer to any digit, including a thumb. Therefore, in someexamples the first finger or the second finger may be a thumb. Movementsof a finger against a surface of the fingerprint sensor 1060 on eitherthe front side or backside of display device 1050 may be used, forexample, to initiate a device wake-up process, authenticate a user,unlock a device, provide a navigational input, select a menu item, startan application, emulate a click or a double-click, move a cursor orpointer, detect a gesture of a user such as a swipe, a flick or a swirl,interact with a browser application, operate a game, change a brightnessor volume, consummate a transaction, initiate a call, operate a camera,or perform another function as described in more detail below withrespect to FIGS. 11 through 17. For example, a control system of thedisplay device 1050 may be configured to recognize data received fromthe fingerprint sensor 1060 as corresponding to patterns that indicatesuch finger movements and/or finger distortions that correspond withfinger exertions. The control system may be configured to cause thedisplay device 1050 to perform one or more of the foregoing functions,or one or more of the functions described below with reference to FIGS.11 through 17, in response to the indication(s) of such finger movementsand/or exertions.

Movements, motions, shear forces and/or normal forces generated by thefinger 506 positioned on the platen 110 of the fingerprint sensor 1060in a direction of arrow 605 may be detected by the fingerprint sensor1060. A control system of the display device 1050 may be configured withthe display 610 to cause corresponding movements of an object 615 in thedirection indicated by arrow 620 such as a movement of an icon, cursoror pointer on a display 610 of the display device 1050. Forces andsequences of forces may be interpreted by a control system of thedisplay device 1050 to navigate, generate one or more mouse functions,cause a screen response, select an application, initiate a function, orotherwise perform a function, some of which are described in more detailbelow with respect to FIGS. 11 through 17.

Accordingly, some mobile device implementations may include a firstfingerprint sensor residing on a first side of the mobile device and adisplay residing on a second side of the mobile device, the second sidebeing opposite from the first side. The first side may be a back sideand the second side may be a front side. The fingerprint sensor mayinclude a platen. The mobile device may include a control systemconfigured for communication with the fingerprint sensor and thedisplay. The control system may be further configured for receivingfingerprint sensor signals from the fingerprint sensor corresponding toa finger positioned on a fingerprint contact area of the platen, fordetecting one or more finger distortions corresponding to changes of thefingerprint sensor signals and for controlling the mobile device based,at least in part, on the distortions. In some implementations, thecontrol system may be configured for detecting a change of thefingerprint contact area and for controlling the mobile device based, atleast in part, on the distortions the detected change of the fingerprintcontact area.

FIG. 11 shows illustrative images that represent translational movements605 of a finger 506 on a platen 110 of a fingerprint sensor andcorresponding navigational inputs. In this example, the fingerprintsensor is a component of an ultrasonic sensor system 102, whereas inother examples the fingerprint sensor may be, or may be a portion of,another type of fingerprint sensor system. A reference position of thefinger 506 may correspond with the initial placement of the finger 506on the platen 110. Directions corresponding to up, down, left, right andcombinations thereof may correspond to translational movements of thefinger 506 on the platen 110, such as may occur when a dry finger or alightly pressed finger is slid along a surface of the platen 110.

In contrast, FIG. 12 shows illustrative images that represent exertionsof a finger 506 that generate shear forces on the platen 110 of afingerprint sensor and corresponding navigational inputs without thefinger 506 sliding on a surface of the platen 110. In this example, thefingerprint sensor is a component of an ultrasonic sensor system 102,whereas in other examples the fingerprint sensor may be, or may be aportion of, another type of fingerprint sensor system. As in FIG. 11, areference position of the finger 506 may correspond with the initialplacement of the finger 506 on the platen 110. Directions correspondingto the direction of arrow 605 such as up, down, left, right andcombinations thereof may correspond to exertions of the finger 506against the platen 110, such as may occur when a finger is heavilypressed against a surface of the platen 110 and where the finger 506fails to slide along the surface of the platen 110, yet deforms inresponse to the lateral physical exertions caused by muscles of the handand fingers that in turn may be detected and interpreted by theultrasonic sensor system 102.

As normal finger forces generally cause the contact area of thefingerprint to change, distortions of the fingerprint ridges and valleysalong with changes in contact area geometry generally occur with thegeneration of shear forces induced by exertions of the finger laterallyagainst the platen surface. FIG. 13 shows illustrative images thatrepresent compressions and expansions of fingerprint ridge spacings thatresult from shear forces generated by exertions of a finger on a platen110 of a fingerprint sensor and corresponding navigational inputs. Thesechanges in fingerprint ridge spacings are further examples of what maybe referred to herein as finger distortions. In this example, thefingerprint sensor is a component of an ultrasonic sensor system 102. Areference position of the finger may correspond with the initialplacement of the finger on the platen 110 that generates a fingerprintcontact area 1308 and associated contact area geometry. Directionscorresponding to up, down, left, right and combinations thereof maycorrespond to movement of the fingerprint contact area 1308′ in thedirection of the arrow 605 or other directions due to exertions of thefinger against the platen 110 where the finger fails to slide orpartially slides along the surface of the platen 110, causingdistortions of the spacings between adjacent fingerprint ridges andchanges to the fingerprint contact area 1308 and associated geometry. Inthe example illustrated, fingerprint ridges 1310 and 1312 near theleading edge of the fingerprint contact area 1308′ are expanded with anincreased fingerprint ridge spacing, whereas fingerprint ridges 1320 and1322 near the trailing edge of the fingerprint contact area 1308′ arecompressed with a decreased fingerprint ridge spacing. Fingerprintridges in other portions of the fingerprint contact area 1308′ such asthose near the center of the contact area may experience little if anydistortion or displacement with lateral exertions of the finger whilethe finger continues to stay in contact with the platen 110 withoutsliding. The fingerprint valley regions may exhibit similar responses asthe fingerprint ridges.

In some implementations, a navigational input may be determined bycomputing a spatial frequency along a set of line segments that areperpendicular to the periphery of a fingerprint contact area. Anelevated spatial frequency may correspond with a compressed set offingerprint ridges, and a decreased spatial frequency may correspondwith an expanded set of fingerprint ridges. For example, spatialfrequencies may be determined along one, two, three, four or more linesegments that are near the periphery of the fingerprint contact area andthe determined spatial frequencies may be compared topreviously-determined spatial frequencies from an earlier point in timeto determine the direction and magnitude of a navigational input.Alternatively, spatial frequencies on one side of a finger contact areamay be compared to one or more spatial frequencies on an opposite sideof the finger contact area, and the difference in the spatialfrequencies may indicate a navigational input. For example, spatialfrequencies on the left side of a finger contact area may be increasedwhile spatial frequencies on the right side of the finger contact areamay be decreased, with the difference indicating a compressed ridgespacing on the left side and an expanded ridge spacing on the right sidethat corresponds with a direction of the navigational input to theright. The magnitude of the difference may indicate the magnitude of thenavigational input.

In some implementations, a measure of the shear force may be determinedby measuring a change in the spacing between sweat pores or otherfingerprint features, particularly those near the periphery of thefingerprint contact area, from which a magnitude and direction of anavigational input may be determined. Fingerprint features that are nearthe periphery of the fingerprint contact area may be referred to asbeing in a peripheral region of the fingerprint contact area. Forexample, an upwardly exerted finger may have stretched fingerprintfeatures near the leading edge of the fingerprint contact area andcompressed fingerprint features near the trailing edge of thefingerprint contact area, from which the direction and magnitude of thenavigational input maybe determined.

FIG. 14 shows illustrative images that represent movement of afingerprint contact area 1308 with respect to one or more fingerprintfeatures 1430, 1432 resulting from shear forces generated by exertionsof a finger on a platen 110 of the fingerprint sensor and correspondingnavigational inputs. In this example, the fingerprint sensor is acomponent of an ultrasonic sensor system 102, whereas in other examplesthe fingerprint sensor may be, or may be a portion of, another type offingerprint sensor system. Fingerprint features 1430, 1432 maycorrespond, for example, to a fingerprint whorl and a bifurcation point,respectively, in a fingerprint image. A reference position of the fingermay correspond with the initial placement of the finger on the platen110 that generates a fingerprint contact area 1308 and associatedcontact area geometry. Directions corresponding to up, down, left, rightand combinations thereof may correspond to movement of the fingerprintcontact area 1308′ in the direction of the arrow 605 or other directionsdue to exertions of the finger against the platen 110 where the fingerfails to slide along the surface of the platen 110, causing changes tothe fingerprint contact area 1308 and associated geometry includingdistances between the periphery of the fingerprint contact area 1308 andthe fingerprint features 1430, 1432. In some implementations,determination of the distances between the periphery of the fingerprintcontact area 1308 and fingerprint features 1430, 1432 in one or moredirections may indicate a navigation function in a preferred directionto be performed.

According to some examples, rotational movements of a finger may bedetected using the multi-functional ultrasonic fingerprint sensor. FIG.15 shows illustrative images that represent rotational movement of afingerprint contact area 1308 with respect to one or more fingerprintfeatures 1430, 1432 resulting from torsional forces generated byexertions of a finger on a platen 110 of a fingerprint sensor andcorresponding navigational inputs. In this example, the fingerprintsensor is a component of an ultrasonic sensor system 102, whereas inother examples the fingerprint sensor may be, or may be a portion of,another type of fingerprint sensor system. In some implementations,rotations clockwise or counterclockwise may be determined by acquiringfingerprint images from the fingerprint sensor, determining the size andshape of a periphery of a reference fingerprint contact area 1308, thenacquiring additional fingerprint images from the fingerprint sensor anddetermining the size and shape of the updated fingerprint contact area1308′ to allow determination of the direction of rotation and the angleof rotation. In the implementation illustrated, fingerprint features1430, 1432 stay fixed (or substantially fixed) in position on the platen110 while the finger is exerted in a twisting, angular motion in thedirection of arrow 605 on the platen 110 without sliding or slipping ofthe fingerprint features 1430, 1432. Other fingerprint features such asridges, valleys and minutiae near the periphery of the updatedfingerprint contact area 1308′ may be analyzed for distortions due toshear stress to determine the desired rotation direction and rotationmagnitude. Determination of rotational motions of the finger may allowinitiating or performing functions such as zoom in, zoom out, increaseor decrease volume, or switch from portrait to landscape view or fromlandscape to portrait view on a display.

Traditional mouse functions such as cursor or pointer navigation,clicking, double-clicking, right-clicking, left-clicking and selectingmay be determined from the multi-functional fingerprint sensor describedabove. FIG. 16 shows illustrative images that represent changingfingerprint contact area 1308 with respect to one or more fingerprintfeatures 1430, 1432 resulting from normal forces generated by exertionsof a finger on a platen 110 of a fingerprint sensor and correspondingnavigational inputs. In this example, the fingerprint sensor is acomponent of an ultrasonic sensor system 102, whereas in other examplesthe fingerprint sensor may be, or may be a portion of, another type offingerprint sensor system. The magnitude of the normal force may bedetermined by acquiring fingerprint images from the fingerprint sensor,determining the size and shape of the fingerprint contact area 1308, andthen correlating the contact area to the applied force. In theimplementation illustrated, fingerprint features 1430, 1432 stay fixedin position on the platen 110 while the finger is pressed with varyinglevels of normal forced in a direction perpendicular to the surface ofthe platen 110, causing the fingerprint contact area 1308′ to enlarge ordecrease in the directions of arrows 625 without sliding or slipping ofthe fingerprint features 1430, 1432 or lifting of the finger from theplate surface. Other fingerprint features such as ridges and valleysnear the periphery of the updated fingerprint contact area 1308′ may beanalyzed for distortions due to shear stress to aid in determining themagnitude of the applied normal force.

FIG. 17 shows representative sequences of forces and motions of a fingerpositioned on a platen of a fingerprint sensor that may be translatedinto predetermined commands for initiating or performing variousfunctions. For example, fingerprint sequence 1701 emulating a short tap(e.g. a “click”) may be determined from the sequence of finger off,light press, heavy press, light press and finger off in relatively quicksuccession. Similarly, a fingerprint sequence emulating a double tap(e.g. a “double-click”) may be determined from the sequence of fingeroff, light press, heavy press, light press, heavy press, light press andfinger off in relatively quick succession. In another example,fingerprint sequence 1702 emulating a long tap may be determined fromthe sequence of finger off, light press, heavy press, several more heavypresses, light press and finger off in somewhat longer succession. Inanother example, fingerprint sequence 1703 emulating a zoom-in or avolume-increase function may be determined from the sequence of fingeroff, light press, heavy press, right rotation, another right rotation,heavy press, light press and finger off. In another example, fingerprintsequence 1704 emulating a zoom-out or a volume-decrease function may bedetermined from the sequence of finger off, light press, heavy press,left rotation, another left rotation, heavy press, light press andfinger off. Other functions may be initiated or performed from otherfingerprint sequences 1705, such as a user log-in function, a wake-uprequest, a kinesthetic password entry, a menu selection input or a userpreference indication. Fingerprint sequences may include a series of oneor more motions with the finger remaining in a non-slipping ornon-sliding mode on the platen surface, a series of one or more motionswith the finger operating in a slip or slide mode, a series of motionsseparated by a finger lift where the finger of a user is temporarilyremoved from the platen surface, or a combination thereof.

FIG. 18 illustrates an augmented ultrasonic sensor array 1803 of anultrasonic sensor system 102 that includes an active ultrasonicfingerprint sensing area 1802 of the ultrasonic sensor array 1803, a setof connective electrical pads 1804, and one or more capacitive senseelectrodes 1806 a, 1806 b for detecting finger position, fingerproximity, finger hydration and/or finger motion. The capacitive senseelectrodes 1806 a, 1806 b may include one or more interdigitatedelectrodes that may be electrically connected to on-chip or off-chipelectronic circuitry via one or more electrical connections 1808 a, 1808b. One or more capacitive sense electrodes 1806 a, 1806 b may be usedfor bioimpedance measurements, such as determination of a capacitiveand/or a resistive component of a finger or other body part at apredetermined frequency. In some implementations, capacitive senseelectrodes 1806 a may be activated with one or more sensor excitationfrequencies and the electrical response such as coupling coefficients,output signal amplitudes and/or phase delays may be determined fromsignals picked up on nearby capacitive sense electrodes 1806 b. Fingerhydration, for example, may impact the effective dielectric permittivitywhen the finger is positioned near the capacitive sense electrodes 1806a, 1806 b. The effective dielectric permittivity may be compared to areference dielectric permittivity, and the comparison may be used as abasis for determining finger hydration. Use of a plurality of differentsensor excitation frequencies allows a spectrum of effective dielectricpermittivities to be determined over a range of frequencies, from whicha finger hydration level, a finger oiliness level, a finger dryness andother property levels such as skin elasticity, skin dryness and skinmoisture may be determined. Bioimpedance measurements obtained from oneor more capacitive sense electrodes 1806 a, 1806 b may augment, supplantor be fused with ultrasonic output signal measurements such as thosedescribed above. Similarly, ultrasonic output signal measurements suchas those described above may augment, supplant or be fused withbioimpedance measurements obtained from one or more capacitive senseelectrodes 1806 a, 1806 b. The bioimpedance measurements may beaugmented with the ultrasonic measurements to obtain more accuratevalues of finger properties such as finger hydration or finger oiliness.In some implementations, a bioimpedance indicator may supplant orreplace an ultrasonically measured finger attribute. In someimplementations, the ultrasonic measurements may be fused oralgorithmically combined with the bioimpedance measurements to increasethe measurement accuracy and/or extend the range of the finger property.For example, a bioimpedance measurement using one or more capacitivesense electrodes 1806 a, 1806 b may be combined with one or moreacoustic impedance measurements from ridge regions and valley regions ofa finger or another body part to obtain a composite measurement thatindicates a skin condition such as skin elasticity. In someimplementations, finger or skin elasticity may be determined from theslope of the fingerprint contact area with a change in finger pressure.With two or more time-sequenced ultrasonic images, the total fingerprintcontact area of a finger positioned against the platen surface may beascertained by determining a set of bounding boxes that include bothfingerprint ridge features and fingerprint valley features, thendetermining the composite area of the set of bounding boxes. Theaggregate ridge area and the aggregate valley area within thefingerprint contact area may be determined. The ratio of aggregate ridgearea to the total fingerprint contact area provides a measure of theapplied finger pressure. In some implementations, the delta outputsignal (e.g., R2−R1) averaged throughout the fingerprint contact areamay provide the measure of applied finger pressure. Additionally, thedelta output signal (e.g., R2−R1) of one or more sensor pixels that arelocated in one or more fingerprint ridge regions provides a measure ofthe acoustic impedance of the finger ridges. A measure of skinelasticity may be determined by dividing the delta output signal in oneor more ridge regions by the ratio of the aggregate ridge area to theoverall fingerprint contact area. In some implementations, the skinelasticity may be determined by dividing the delta output signal in oneor more ridge regions by the delta output signal in the fingerprintcontact area. The skin elasticity in turn may be determined from thecalculated slope by including appropriate calibration and unitconversion multipliers. The ultrasonic fingerprint sensor may be usedwith other portions of the body for determining skin hydration, skinoiliness, skin elasticity or other skin conditions of the other bodyportions, such as placing the platen of the ultrasonic fingerprintsensor against a portion of the face, neck, arm or leg.

Finger temperature or the temperature of a target object positioned onor near the ultrasonic sensor array 1803 may be determined from atemperature sensing device 1810 such as a resistive temperature device,a semiconductor device such as a reverse-biased diode, or athermocouple. The temperature sensing device 1810 may be electricallyconnected to on-chip or off-chip electronic circuitry via electricalconnections 1812 a, 1812 b. Multi-functional ultrasonic fingerprintsensors may combine one or more sensor types along with ultrasonicimaging capabilities to determine biometric and health attributes of auser, such as in a medical diagnostic device, an activity monitor, or amulti-functional sports watch.

In some implementations, one or more biometric indicators generated frombioimpedance measurements using one or more capacitive sense electrodes1806 a, 1806 b of the augmented ultrasonic sensor array 1803 may becombined with the results of a user authentication process using datareceived from the ultrasonic sensor array 1803 to provide two-factor ormulti-factor authentication of a user. Biometric indicators generatedfrom the bioimpedance measurements may include a moisture level of afinger of an authorized user. Some implementations may generatebiometric indicators based on a finger hydration level, a fingeroiliness level, a finger dryness level, a skin elasticity level or otherfinger property level. A biometric indicator may be affirmed if thebiometric indicator lies above a predetermined lower biometricthreshold, below a predetermined upper biometric threshold, or within apredetermined biometric range. In some implementations, thepredetermined biometric thresholds and/or ranges may be determined froma population of test subjects and stored as one or more calibrationparameters at a factory during testing and assembling of the fingerprintsensor system. In some implementations, the biometric thresholds and/orranges may be determined from an enrolled finger of an authorized userduring an enrollment procedure with the authorized user's finger. Insome implementations, the biometric thresholds and/or ranges may bestored with other fingerprint and/or attribute information in one ormore enrollment templates for later use in a user authentication orvalidation process.

A liveness indicator may be determined from one or more biometricindicators generated from the bioimpedance measurements. The livenessindicator may be combined with the results of a user authentication orvalidation process to provide a higher level of confidence in theauthentication/validation result. The status of the liveness indicatormay be provided to the proposed user of a mobile device, particularly ifthe status of the liveness indicator is false (indicating that a targetobject is not alive), negative or non-affirmed. In some implementations,the status of the liveness indicator may be provided to an authorizeduser or to a network-connected device, and/or stored for laterconveyance to the authorized user, the network-connected device, or tothe authorities. In some implementations, the liveness indicator may bebased on a moisture content of a target object such as a finger placedon a platen of the fingerprint sensor system. In some implementations,the liveness indicator may be based on a finger hydration level, afinger oiliness level, a finger dryness level, a skin elasticity level,a finger hydration-to-oiliness ratio, a finger hydration-to-oilinesscorrelation, or other finger property level or ratio of property levels.In some implementations, the basis for the liveness indicator mayinclude one or more minimum threshold values, one or more maximumthreshold values, or one or more biometric ranges.

Bioimpedance measurements from the one or more capacitive senseelectrodes 1806 a, 1806 b of the augmented ultrasonic sensor array 1803may provide algorithmic improvements to fingerprint data as part of anauthentication process. The authentication process may involve obtaining(e.g., via a control system) current fingerprint data and comparing thecurrent fingerprint data with stored fingerprint data of an enrolleduser. The fingerprint data may be derived from fingerprint sensorsignals, which in some implementations may include ultrasonic sensorsignals. According to some examples, the fingerprint data may includekeypoints, fingerprint minutiae and/or fingerprint ridge flow patterns.For example, during different times of the day, a user's finger may bedrier than at other times. In more severe situations, finger dryness mayresult in discontinuous sections of a fingerprint ridge that maynormally be connected during normal finger hydration levels such asafter washing hands with soap or exposure to alcohol-based disinfectantwipes. In some cases, a user's finger may exhibit a larger number ofislands, segmented ridges or discontinuous ridges along one or morefingerprint ridge regions during low-hydration periods than duringnormal moisture-level periods. According to some examples, anauthentication process may involve modifying (e.g., via a controlsystem) the current fingerprint data according to bioimpedancemeasurements, to produce modified current fingerprint data, andcomparing the modified current fingerprint data with stored fingerprintdata of an enrolled user. Alternatively, or additionally, in someimplementations a fingerprint matching process may be adjusted accordingto bioimpedance measurements. In some implementations, bioimpedancemeasurements that indicate excessive dryness may allow the fingerprintmatching algorithms to adjust various keypoints, fingerprint minutiae orfingerprint ridge flow patterns according to bioimpedance measurements.In some implementations, the threshold values for a fingerprint matchmay be adjusted for finger dryness and image quality reductions that mayoccur when an enrolled finger is particularly dry. Variations in fingerdryness with seasonal changes and exposure to humid or non-humidenvironments such as a warm shower or a cold winter day may beaccommodated by the fingerprint matching algorithms using thebioimpedance measurements. Tendencies for increased finger dryness withage may also be accommodated. Other biometric indicators generated frombioimpedance measurements such as finger hydration or finger oilinessmay impact the image quality or fingerprint features and be accommodatedby the fingerprint matching algorithms.

Excessively wet fingers can present difficulties to fingerprint matchingalgorithms due in part to the softening and enlarging of fingerprintridges with increased hydration and the possibility of fingerprintvalley regions filling in with water. Bioimpedance measurements from oneor more capacitive sense electrodes 1806 a, 1806 b of the ultrasonicsensor array 1803 may be incorporated into the fingerprint matchingalgorithms and adjustments to fingerprint features or image quality bemade accordingly. In a similar manner, excessively oily fingers canpresent difficulties to fingerprint matching algorithms due in part tothe reduction of fingerprint features that may occur with increasedexposure to lotions or other oily substances. Bioimpedance measurementsmay be incorporated into the fingerprint matching algorithms andadjustments made accordingly to fingerprint features or image qualityaspects.

Input from the ultrasonic sensor array 1803 may, in some examples, beused (for example, by a control system) to modify, extend the range of,or otherwise augment bioimpedance measurements from the one or morecapacitive sense electrodes 1806 a, 1806 b. For example, the range ofhydration and oiliness levels from the bioimpedance measurements may beextended at either the low end or high end of the finger hydrationand/or finger oiliness range by incorporating acoustic impedancemeasurements from the ultrasonic sensor array. For example, a change inacoustic impedance indicates a change in the speed of sound and/or massdensity of the fingerprint ridge regions and other regions of the fingerthat can be correlated to and increase the accuracy of the bioimpedancemeasurements within a particular range or to enhance the range of validskin temperature, skin hydration, skin moisture, skin dryness, skinoiliness, skin condition or other skin levels.

In some implementations, determining the contact area of the fingerprintmay provide an indication of when a bioimpedance measurement is valid.For example, a sufficiently high fingerprint contact area from theultrasonic image information may indicate sufficient contact force toobtain an accurate bioimpedance measurement. The contact forcedetermination may be used to provide auditory or visual feedback to auser (e.g., via one or more elements of a user interface system, such asa speaker and/or a display) on whether to press harder on the sensorplaten. The contact force determination may be used to determine when toapply a plurality of different sensor excitation frequencies from whichhydration level, oiliness level, dryness level and other property levelssuch as skin elasticity, skin dryness and skin moisture may bedetermined. In some implementations, the ultrasonic image informationmay be used to determine that a finger is correctly placed on the sensorand to notify a user accordingly. In some implementations, theultrasonic image information may be used to indicate a wet-fingercondition and correct the finger hydration levels accordingly.

In some implementations, acquired ultrasonic image data may be used toindicate which of one or more capacitive sense electrodes 1806 a, 1806 bshould be used in determination of the bioimpedance indicators. In someimplementations, bioimpedance measurements from two or more sets ofcapacitive sense electrodes 1806 a, 1806 b may be weighted by the degreein which a finger is positioned over the various capacitive senseelectrodes 1806 a, 1806 b when determining the bioimpedance indicators.

In some implementations, the ultrasonic sensor array may be used toacquire depth-related (such as three-dimensional or 3-D) image datawithin a finger or other body part. Some examples are described belowwith reference to FIG. 21. The capacitive sense electrodes 1806 a, 1806b may be used to determine levels of finger hydration and other tissuecharacteristics that allow the extraction of acoustic information suchas acoustic attenuation and local speed of sound. The acousticinformation may be used in turn to correct, enhance, or otherwise modifythe 3-D ultrasonic image data so that signals from deeper portions of afinger may be corrected accordingly for enhanced depth-profiling, 3-Dimaging and user authentication.

FIG. 19 representationally depicts aspects of a 4×4 pixel array ofsensor pixels for an ultrasonic sensor system. Each sensor pixel 1934may be, for example, associated with a local region of piezoelectricsensor material (PSM), a pixel input electrode 1937, a peak detectiondiode (D1) and a readout transistor (M3); many or all of these elementsmay be formed on or in a substrate to form the pixel circuit 1936. Inpractice, the local region of piezoelectric sensor material of eachsensor pixel 1934 may transduce received ultrasonic energy intoelectrical charges. The peak detection diode D1 may register the maximumamount of charge detected by the local region of piezoelectric sensormaterial PSM. Each row of the pixel array 1935 may then be scanned,e.g., through a row select mechanism, a gate driver, or a shiftregister, and the readout transistor M3 for each column may be triggeredto allow the magnitude of the peak charge for each sensor pixel 1934 tobe read by additional circuitry, e.g., a multiplexer and an A/Dconverter. The pixel circuit 1936 may include one or more TFTs to allowgating, addressing, and resetting of the sensor pixel 1934.

Each pixel circuit 1936 may provide information about a small portion ofthe object detected by the ultrasonic sensor system. While, forconvenience of illustration, the example shown in FIG. 19 is of arelatively coarse resolution, ultrasonic sensors having a resolution onthe order of 500 pixels per inch or higher may be configured with anappropriately scaled structure. The detection area of the ultrasonicsensor system may be selected depending on the intended object ofdetection. For example, the detection area may range from about 8 mm×3mm, 5 mm×5 mm or 9 mm×4 mm for a single finger to about 3 inches×3inches for four fingers. Smaller and larger areas, including square,rectangular and non-rectangular geometries, may be used as appropriatefor the target object.

FIG. 20A shows an example of an exploded view of an ultrasonic sensorsystem. In this example, the ultrasonic sensor system 2000 a includes anultrasonic transmitter 20 and an ultrasonic receiver 30 under a platen40. According to some implementations, the ultrasonic receiver 30 may bean example of the ultrasonic sensor array 103 that is shown in FIG. 1and described above. In some implementations, the ultrasonic transmitter20 may be an example of the ultrasonic transmitter 105 that is shown inFIG. 1 and described above. The ultrasonic transmitter 20 may include asubstantially planar piezoelectric transmitter layer 22 and may becapable of functioning as a plane wave generator. Ultrasonic waves maybe generated by applying a voltage to the piezoelectric layer to expandor contract the layer, depending upon the signal applied, therebygenerating a plane wave. In this example, the control system 106 may becapable of causing a voltage that may be applied to the planarpiezoelectric transmitter layer 22 via a first transmitter electrode 24and a second transmitter electrode 26. In this fashion, an ultrasonicwave may be made by changing the thickness of the layer via apiezoelectric effect. This generated ultrasonic wave may travel towardsa finger (or other object to be detected), passing through the platen40. A portion of the wave not absorbed or transmitted by the object tobe detected may be reflected so as to pass back through the platen 40and be received by the ultrasonic receiver 30. The first and secondtransmitter electrodes 24 and 26 may be metallized electrodes, forexample, metal layers that coat opposing sides of the piezoelectrictransmitter layer 22.

The ultrasonic receiver 30 may include an array of sensor pixel circuits32 disposed on a substrate 34, which also may be referred to as abackplane, and a piezoelectric receiver layer 36. In someimplementations, each sensor pixel circuit 32 may include one or moreTFT- or silicon-based elements, electrical interconnect traces and, insome implementations, one or more additional circuit elements such asdiodes, capacitors, and the like. Each sensor pixel circuit 32 may beconfigured to convert surface charge generated by the piezoelectricreceiver layer 36 proximate to the pixel circuit into an electricalsignal. Each sensor pixel circuit 32 may include a pixel input electrode38 that electrically couples the piezoelectric receiver layer 36 to thesensor pixel circuit 32.

In the illustrated implementation, a receiver bias electrode 39 isdisposed on a side of the piezoelectric receiver layer 36 proximal toplaten 40. The receiver bias electrode 39 may be a metallized electrodeand may be grounded or biased to control which signals may be passed tothe array of sensor pixel circuits 32. Ultrasonic energy that isreflected from the exposed (top) surface of the platen 40 may beconverted into surface charge by the piezoelectric receiver layer 36.The generated surface charge may be coupled to the pixel inputelectrodes 38 and underlying sensor pixel circuits 32. The charge signalmay be amplified or buffered by the sensor pixel circuits 32 andprovided to the control system 106.

The control system 106 may be electrically connected (directly orindirectly) with the first transmitter electrode 24 and the secondtransmitter electrode 26, as well as with the receiver bias electrode 39and the sensor pixel circuits 32 on the substrate 34. In someimplementations, the control system 106 may operate substantially asdescribed above. For example, the control system 106 may be capable ofprocessing the amplified signals received from the sensor pixel circuits32.

The control system 106 may be capable of controlling the ultrasonictransmitter 20 and/or the ultrasonic receiver 30 to obtain ultrasonicdata, which may include fingerprint data. According to someimplementations, the control system 106 may be capable of providingfunctionality such as that described herein with reference to FIGS.1-18.

Whether or not the ultrasonic sensor system 2000 a includes a separateultrasonic transmitter 20, in some implementations the control system106 may be capable of obtaining attribute information from theultrasonic data. In some examples, the control system 106 may be capableof controlling access to one or more devices based, at least in part, onthe attribute information. The ultrasonic sensor system 2000 a (or anassociated device) may include a memory system that includes one or morememory devices. In some implementations, the control system 106 mayinclude at least a portion of the memory system. The control system 106may be capable of obtaining attribute information from ultrasonic dataand storing the attribute information in the memory system. In someimplementations, the control system 106 may be capable of capturing afingerprint image, obtaining attribute information from the fingerprintimage and storing attribute information obtained from the fingerprintimage (which may be referred to herein as fingerprint image information)in the memory system. According to some examples, the control system 106may be capable of capturing a fingerprint image, obtaining attributeinformation from the fingerprint image and storing attribute informationobtained from the fingerprint image even while maintaining theultrasonic transmitter 20 in an “off” state.

In some implementations, the control system 106 may be capable ofoperating the ultrasonic sensor system 2000 a in an ultrasonic imagingmode or a force-sensing mode. In some implementations, the controlsystem may be capable of maintaining the ultrasonic transmitter 20 in an“off” state when operating the ultrasonic sensor system in aforce-sensing mode. The ultrasonic receiver 30 may be capable offunctioning as a force sensor when the ultrasonic sensor system 2000 ais operating in the force-sensing mode. In some implementations, thecontrol system 106 may be capable of controlling other devices, such asa display system, a communication system, etc. In some implementations,the control system 106 may be capable of operating the ultrasonic sensorsystem 2000 a in a capacitive imaging mode.

The platen 40 may be any appropriate material that can be acousticallycoupled to the receiver, with examples including plastic, ceramic,sapphire, metal and glass. In some implementations, the platen 40 may bea cover plate, e.g., a cover glass or a lens glass for a display.Particularly when the ultrasonic transmitter 20 is in use, fingerprintdetection and imaging can be performed through relatively thick platensif desired, e.g., 3 mm and above. However, for implementations in whichthe ultrasonic receiver 30 is capable of imaging fingerprints in a forcedetection mode or a capacitance detection mode, a thinner and relativelymore compliant platen 40 may be desirable. According to some suchimplementations, the platen 40 may include one or more polymers, such asone or more types of parylene, and may be substantially thinner. In somesuch implementations, the platen 40 may be tens of microns thick or evenless than 10 microns thick.

Examples of piezoelectric materials that may be used to form thepiezoelectric receiver layer 36 include piezoelectric polymers havingappropriate acoustic properties, for example, an acoustic impedancebetween about 2.5 MRayls and 5 MRayls. Specific examples ofpiezoelectric materials that may be employed include ferroelectricpolymers such as polyvinylidene fluoride (PVDF) and polyvinylidenefluoride-trifluoroethylene (PVDF-TrFE) copolymers. Examples of PVDFcopolymers include 60:40 (molar percent) PVDF-TrFE, 70:30 PVDF-TrFE,80:20 PVDF-TrFE, and 90:10 PVDR-TrFE. Other examples of piezoelectricmaterials that may be employed include polyvinylidene chloride (PVDC)homopolymers and copolymers, polytetrafluoroethylene (PTFE) homopolymersand copolymers, and diisopropylammonium bromide (DIPAB).

The thickness of each of the piezoelectric transmitter layer 22 and thepiezoelectric receiver layer 36 may be selected so as to be suitable forgenerating and receiving ultrasonic waves. In one example, a PVDF planarpiezoelectric transmitter layer 22 is approximately 28 μm thick and aPVDF-TrFE receiver layer 36 is approximately 12 μm thick. Examplefrequencies of the ultrasonic waves may be in the range of 5 MHz to 30MHz, with wavelengths on the order of a millimeter or less.

FIG. 20B shows an exploded view of an alternative example of anultrasonic sensor system. In this example, the piezoelectric receiverlayer 36 has been formed into discrete elements 37. In theimplementation shown in FIG. 20B, each of the discrete elements 37corresponds with a single pixel input electrode 38 and a single sensorpixel circuit 32. However, in alternative implementations of theultrasonic sensor system 2000 b, there is not necessarily a one-to-onecorrespondence between each of the discrete elements 37, a single pixelinput electrode 38 and a single sensor pixel circuit 32. For example, insome implementations there may be multiple pixel input electrodes 38 andsensor pixel circuits 32 for a single discrete element 37.

FIGS. 20A and 20B show example arrangements of ultrasonic transmittersand receivers in an ultrasonic sensor system, with other arrangementsbeing possible. For example, in some implementations, the ultrasonictransmitter 20 may be above the ultrasonic receiver 30 and thereforecloser to the object(s) to be detected. In some implementations, theultrasonic transmitter may be included with the ultrasonic sensor array(e.g., a single-layer transmitter and receiver). In someimplementations, the ultrasonic sensor system may include an acousticdelay layer. For example, an acoustic delay layer may be incorporatedinto the ultrasonic sensor system between the ultrasonic transmitter 20and the ultrasonic receiver 30. An acoustic delay layer may be employedto adjust the ultrasonic pulse timing, and at the same time electricallyinsulate the ultrasonic receiver 30 from the ultrasonic transmitter 20.The acoustic delay layer may have a substantially uniform thickness,with the material used for the delay layer and/or the thickness of thedelay layer selected to provide a desired delay in the time forreflected ultrasonic energy to reach the ultrasonic receiver 30. Indoing so, the range of time during which an energy pulse that carriesinformation about the object by virtue of having been reflected by theobject may be made to arrive at the ultrasonic receiver 30 during a timerange when it is unlikely that energy reflected from other parts of theultrasonic sensor system is arriving at the ultrasonic receiver 30. Insome implementations, the substrate 34 and/or the platen 40 may serve asan acoustic delay layer,

FIG. 20C shows an exploded view of an example of an ultrasonic sensorsystem. In this example, the ultrasonic sensor system 2000 c includes anultrasonic transceiver array 50 under a platen 40. According to someimplementations, the ultrasonic transceiver array 50 may serve as boththe ultrasonic sensor array 103 and the ultrasonic transmitter 105 thatis shown in FIG. 1 and described above. The ultrasonic transceiver array50 may include a substantially planar piezoelectric transceiver layer 56capable of functioning as a plane wave generator. Ultrasonic waves maybe generated by applying a voltage across the transceiver layer 56. Thecontrol system 106 may be capable of generating a transceiver excitationvoltage that may be applied to the piezoelectric transceiver layer 56via one or more underlying pixel input electrodes 38 or one or moreoverlying transceiver bias electrodes 59. The generated ultrasonic wavemay travel towards a finger or other object to be detected, passingthrough the platen 40. A portion of the wave not absorbed or transmittedby the object may be reflected so as to pass back through the platen 40and be received by the ultrasonic transceiver array 50.

The ultrasonic transceiver array 50 may include an array of sensor pixelcircuits 32 disposed on a substrate 34. In some implementations, eachsensor pixel circuit 32 may include one or more TFT- or silicon-basedelements, electrical interconnect traces and, in some implementations,one or more additional circuit elements such as diodes, capacitors, andthe like. Each sensor pixel circuit 32 may include a pixel inputelectrode 38 that electrically couples the piezoelectric transceiverlayer 56 to the sensor pixel circuit 32.

In the illustrated implementation, the transceiver bias electrode 59 isdisposed on a side of the piezoelectric transceiver layer 56 proximal tothe platen 40. The transceiver bias electrode 59 may be a metallizedelectrode and may be grounded or biased to control which signals may begenerated and which reflected signals may be passed to the array ofsensor pixel circuits 32. Ultrasonic energy that is reflected from theexposed (top) surface of the platen 40 may be converted into surfacecharge by the piezoelectric transceiver layer 56. The generated surfacecharge may be coupled to the pixel input electrodes 38 and underlyingsensor pixel circuits 32. The charge signal may be amplified or bufferedby the sensor pixel circuits 32 and provided to the control system 106.

The control system 106 may be electrically connected (directly orindirectly) to the transceiver bias electrode 59 and the sensor pixelcircuits 32 on the sensor substrate 34. In some implementations, thecontrol system 106 may operate substantially as described above. Forexample, the control system 106 may be capable of processing theamplified signals received from the sensor pixel circuits 32.

The control system 106 may be capable of controlling the ultrasonictransceiver array 50 to obtain ultrasonic data, which may includefingerprint data. According to some implementations, the control system106 may be capable of providing functionality such as that describedherein, e.g., such as described herein with reference to FIGS. 1-18.

In other examples of an ultrasonic sensor system with an ultrasonictransceiver array, a backside of the sensor substrate 34 may be attacheddirectly or indirectly to an overlying platen 40. In operation,ultrasonic waves generated by the piezoelectric transceiver layer 56 maytravel through the sensor substrate 34 and the platen 40, reflect off asurface of the platen 40, and travel back through the platen 40 and thesensor substrate 34 before being detected by sensor pixel circuits 32 onor in the substrate sensor 34.

FIG. 21 shows examples of multiple acquisition time delays beingselected to receive acoustic waves reflected from different depths. Suchexamples may be advantageous for acquiring ultrasonic data for a 3-Dimage, e.g., for a 3-D fingerprint image. In these examples, each of theacquisition time delays (which are labeled range-gate delays or RGDs inFIG. 21) is measured from the beginning time t₁ of the transmittedsignal 2105 shown in graph 2100. The graph 2110 depicts reflectedacoustic waves (received wave (1) is one example) that may be receivedby an ultrasonic sensor array at an acquisition time delay RGD₁ andsampled during an acquisition time window of RGW₁. Such acoustic waveswill generally be reflected from a relatively shallower portion of atarget object proximate, or positioned upon, a platen of the biometricsystem.

Graph 2115 depicts reflected acoustic waves (received wave (2) is oneexample) that are received by at least a portion of the ultrasonicsensor array at an acquisition time delay RGD₂ (with RGD₂>RGD₁) andsampled during an acquisition time window of RGW₂. Such acoustic waveswill generally be reflected from a relatively deeper portion of thetarget object. Graph 2120 depicts reflected acoustic waves (receivedwave (n) is one example) that are received at an acquisition time delayRGD_(n) (with RGD_(n)>RGD₂>RGD₁) and sampled during an acquisition timewindow of RGW_(n). Such acoustic waves will generally be reflected froma still deeper portion of the target object.

Range-gate delays are typically integer multiples of a clock period. Aclock frequency of 128 MHz, for example, has a clock period of 7.8125nanoseconds, and RGDs may range from under 10 nanoseconds to over 20,000nanoseconds.

Similarly, the range-gate windows may also be integer multiples of theclock period, but are often much shorter than the RGD (e.g. less thanabout 50 nanoseconds) to capture returning signals while retaining goodaxial resolution. In some implementations, the acquisition time window(RGW) may be between about 10 nanoseconds to about 200 nanoseconds. Insome examples, the RGW may be less than 10 nanoseconds, e.g., 5nanoseconds, 6 nanoseconds, 7 nanoseconds or 8 nanoseconds. Suchimplementations may be advantageous for acquiring ultrasonic data for a3-D image, e.g., for a 3-D fingerprint image. However, in some examplesthe RGW may be more than 200 nanoseconds.

Extending the duration of the range-gate width while keeping the RGDconstant allows the sensor pixel circuits to capture the peak value ofthe reflected ultrasonic waves corresponding to the fingerprint ridgesand valleys and to sub-epidermal features that may be captured duringthe time that the RGW is active. Increasing the RGD allows imaging ofsub-epidermal features deeper into the finger.

Note that while various image bias levels (e.g. Tx block, Rx sample andRx hold that may be applied to an Rx bias electrode) may be in thesingle or low double-digit volt range, the return signals may havevoltages in the tens or hundreds of millivolts. In some implementations,the receiver bias control signal having two or more levels representingthe selected RGD and RGW may be applied to the receiver bias electrodeof the ultrasonic sensor array. In some implementations, a diode biascontrol signal applied to the sensor pixel circuits within theultrasonic sensor array may contain two or more levels representing theselected RGD and RGW. In some implementations, a portion of the sensorpixel circuits, such as a block, line or sub-array of pixels, may beused to acquire one or more images in a sub-surface region of the targetobject at the desired depth and position to increase the frame rate andreduce the image processing requirements.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso may be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium, such as a non-transitory medium. The processesof a method or algorithm disclosed herein may be implemented in aprocessor-executable software module which may reside on acomputer-readable medium. Computer-readable media include both computerstorage media and communication media including any medium that may beenabled to transfer a computer program from one place to another.Storage media may be any available media that may be accessed by acomputer. By way of example, and not limitation, non-transitory mediamay include RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that may be used to store desired program code in the form ofinstructions or data structures and that may be accessed by a computer.Also, any connection may be properly termed a computer-readable medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk, and blu-raydisc where disks usually reproduce data magnetically, while discsreproduce data optically with lasers. Combinations of the above shouldalso be included within the scope of computer-readable media.Additionally, the operations of a method or algorithm may reside as oneor any combination or set of codes and instructions on a machinereadable medium and computer-readable medium, which may be incorporatedinto a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those having ordinary skill in theart, and the generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein, if atall, to mean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.

Certain features that are described in this specification in the contextof separate implementations also may be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also may be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemsmay generally be integrated together in a single software product orpackaged into multiple software products. Additionally, otherimplementations are within the scope of the following claims. In somecases, the actions recited in the claims may be performed in a differentorder and still achieve desirable results.

It will be understood that unless features in any of the particulardescribed implementations are expressly identified as incompatible withone another or the surrounding context implies that they are mutuallyexclusive and not readily combinable in a complementary and/orsupportive sense, the totality of this disclosure contemplates andenvisions that specific features of those complementary implementationsmay be selectively combined to provide one or more comprehensive, butslightly different, technical solutions. It will therefore be furtherappreciated that the above description has been given by way of exampleonly and that modifications in detail may be made within the scope ofthis disclosure.

The invention claimed is:
 1. An apparatus, comprising: an ultrasonicsensor system; a platen; a set of bioimpedance electrodes proximate theplaten; and a control system comprising one or more processors, thecontrol system being configured for communication with the ultrasonicsensor system and the set of bioimpedance electrodes, the control systemfurther configured for: controlling the ultrasonic sensor system totransmit ultrasonic waves; receiving ultrasonic sensor signals from theultrasonic sensor system corresponding to ultrasonic waves reflectedfrom a portion of a body in contact with the platen, wherein the portionof the body comprises a finger; receiving bioimpedance measurements fromthe set of bioimpedance electrodes; determining a liveness indicatorbased, at least in part, on the bioimpedance measurements; andperforming an authentication process based, at least in part, on theultrasonic sensor signals and the liveness indicator, wherein theauthentication process involves: determining current fingerprint databased on the ultrasonic sensor signals; modifying the currentfingerprint data according to the bioimpedance measurements, to producemodified current fingerprint data; and comparing the modified currentfingerprint data with stored fingerprint data of an enrolled user. 2.The apparatus of claim 1, wherein the control system is configured fordetermining changes in at least one of capacitance or resistance of theportion of the body according to changes of the bioimpedancemeasurements.
 3. The apparatus of claim 1, wherein the one or morebiometric indicators include at least one biometric indicator selectedfrom a list of biometric indicators consisting of skin hydration level,skin oiliness level, skin dryness and skin elasticity.
 4. The apparatusof claim 1, wherein the control system is configured to modify one ormore of the bioimpedance measurements according to the ultrasonic sensorsignals.
 5. The apparatus of claim 1, wherein the bioimpedanceelectrodes include capacitive sense electrodes.
 6. The apparatus ofclaim 5, wherein the capacitive sense electrodes include interdigitatedcapacitive sense electrodes.
 7. The apparatus of claim 5, wherein thecontrol system is configured for: activating a first subset of thecapacitive sense electrodes with one or more sensor excitationfrequencies; and receiving an electrical response from a second subsetof the capacitive sense electrodes.
 8. The apparatus of claim 7, whereinthe electrical response includes an output signal amplitude, a phasedelay, or both an output signal amplitude and a phase delay.
 9. Theapparatus of claim 7, wherein the control system is further configuredfor estimating a status of one or more biometric indicators of theportion of the body based on the ultrasonic sensor signals and thebioimpedance measurements, wherein estimating the status of the one ormore biometric indicators involves determining an effective dielectricpermittivity of the portion of the body and comparing the effectivedielectric permittivity with a reference dielectric permittivity. 10.The apparatus of claim 7, wherein the control system is configured for:activating the first subset of the capacitive sense electrodes with aplurality of sensor excitation frequencies; determining a plurality ofeffective dielectric permittivities of the portion of the body, each ofthe plurality of effective dielectric permittivities corresponding to asensor excitation frequency of the plurality of sensor excitationfrequencies; and comparing the effective dielectric permittivities withreference dielectric permittivities.
 11. The apparatus of claim 1,wherein the control system is configured for: calculating, based on theultrasonic sensor signals, one or more acoustic impedance values for theportion of the body; and estimating a status of the one or morebiometric indicators based on the one or more acoustic impedance valuesand the bioimpedance measurements.
 12. The apparatus of claim 11,wherein the control system is configured for: calculating a compositemeasurement based on the one or more acoustic impedance values and thebioimpedance measurements; and determining a skin condition of theportion of the body based, at least in part, on the compositemeasurement.
 13. The apparatus of claim 1, further comprising asubstrate, wherein the set of bioimpedance electrodes and ultrasonicsensors of the ultrasonic sensor system reside on the substrate.
 14. Theapparatus of claim 1, wherein the control system is configured for:determining, based on the ultrasonic sensor signals, a fingerprintcontact area, and estimating a status of one or more biometricindicators of the portion of the body based on the ultrasonic sensorsignals and the bioimpedance measurements, wherein estimating the statusof one or more biometric indicators is based, at least in part, on thefingerprint contact area.
 15. The apparatus of claim 14, wherein theapparatus includes a user interface system and wherein the controlsystem is configured to provide feedback, via the user interface system,regarding the fingerprint contact area.
 16. The apparatus of claim 1,wherein the authentication process is also based on a biometricindicator and wherein the control system is configured for generatingthe biometric indicator from the bioimpedance measurements.
 17. Theapparatus of claim 16, wherein the authentication process involves oneor more of determining whether the biometric indicator upon which theauthentication process is based, in part, is above a predetermined lowerbiometric threshold, determining whether the biometric indicator isbelow a predetermined upper biometric threshold, or determining whetherthe biometric indicator is within a predetermined biometric range. 18.The apparatus of claim 1, wherein modifying the current fingerprint datainvolves one or more corrections selected from a list of correctionsconsisting of a ridge-flow correction, a dry-finger correction, awet-finger correction and an oily-finger correction.
 19. The apparatusof claim 1, wherein the authentication process involves: determiningcurrent fingerprint data based on the ultrasonic sensor signals;adjusting a fingerprint matching process according to the bioimpedancemeasurements; and comparing, according to the adjusted fingerprintmatching process, the current fingerprint data with stored fingerprintdata of an enrolled user.
 20. The apparatus of claim 1, wherein thecontrol system is configured for: controlling the ultrasonic sensorsystem to obtain three-dimensional image data; extracting acousticinformation from the bioimpedance measurements; and modifying thethree-dimensional image data according to the acoustic information. 21.A method, comprising: controlling an ultrasonic sensor system totransmit ultrasonic waves; receiving ultrasonic sensor signals from theultrasonic sensor system corresponding to ultrasonic waves reflectedfrom a portion of a body in contact with the platen, wherein the portionof the body comprises a finger; receiving bioimpedance measurements fromthe set of bioimpedance electrodes; determining a liveness indicatorbased, at least in part, on the bioimpedance measurements; andperforming an authentication process based, at least in part, on theultrasonic sensor signals and the liveness indicator, wherein theauthentication process involves: determining current fingerprint databased on the ultrasonic sensor signals; modifying the currentfingerprint data according to the bioimpedance measurements, to producemodified current fingerprint data; and comparing the modified currentfingerprint data with stored fingerprint data of an enrolled user. 22.The method of claim 21, further comprising estimating a status of one ormore biometric indicators of the portion of the body based on theultrasonic sensor signals and the bioimpedance measurements, wherein theone or more biometric indicators include at least one biometricindicator selected from a list of biometric indicators consisting ofskin hydration level, skin oiliness level, skin dryness and skinelasticity.
 23. The method of claim 21, wherein the bioimpedanceelectrodes include capacitive sense electrodes and wherein the methodfurther comprises: activating a first subset of the capacitive senseelectrodes with one or more sensor excitation frequencies; and receivingan electrical response from a second subset of the capacitive senseelectrodes.
 24. A non-transitory medium having software stored thereon,the software including instructions for: controlling an ultrasonicsensor system to transmit ultrasonic waves; receiving ultrasonic sensorsignals from the ultrasonic sensor system corresponding to ultrasonicwaves reflected from a portion of a body; receiving bioimpedancemeasurements from a set of bioimpedance electrodes; controlling theultrasonic sensor system to obtain three-dimensional image data;extracting acoustic information from the bioimpedance measurements; andmodifying the three-dimensional image data according to the acousticinformation.
 25. The non-transitory medium of claim 24, wherein thesoftware includes instructions for: determining a liveness indicatorbased, at least in part, on the bioimpedance measurements; andperforming an authentication process based, at least in part, on theultrasonic sensor signals and the liveness indicator.
 26. An apparatus,comprising: an ultrasonic sensor system; a platen; a set of bioimpedanceelectrodes proximate the platen; and control means configured forcommunication with the ultrasonic sensor system and the set ofbioimpedance electrodes, the control means comprising means for:controlling the ultrasonic sensor system to transmit ultrasonic waves;receiving bioimpedance measurements from a set of bioimpedanceelectrodes; controlling the ultrasonic sensor system to obtainthree-dimensional image data; extracting acoustic information from thebioimpedance measurements; and modifying the three-dimensional imagedata according to the acoustic information.
 27. The apparatus of claim26, wherein the control means includes means for determining changes inat least one of capacitance or resistance of the portion of the bodyaccording to changes of the bioimpedance measurements.